I've been trying to learn to play the keyboard for a few years now and think it would be cool to eventually get to the point where am able to play as part of a group. The problem is that I really have no idea how to go about reaching this goal.

This makes it seem that you'd like to practice alone at home, until you know everything and can come out as a fully trained keyboard player, without having to face other people as a not-yet-fully-competent beginner. Sort of like, wanting to learn a language completely before trying to speak with anyone. But the thing is, you learn to play keyboard parts in a band by playing keyboard parts in a band. Go there and try something, and your learning will be boosted to a completely new level. One hour of actual real playing is worth ten hours of practicing alone.

I'd think that a good way to practice would be by taking songs and simply playing them the way I would be expected to play them in a band. The problem is that I really don't know what that would be.

I think there's a mistake here. You're looking at entire songs, when you should be looking at keyboard parts of song arrangements. Look at what keyboard players do in bands.

There are many different categories of things keyboard players do. On an abstract level, the parts can be looked at from several perspectives: rhythm, harmony, pitch, texture, or the overall big story of a song. Or melody which has aspects of all of those. On a less abstract level you could think about things like (1) rhythmic comping, (2) background pads, (3) melodic playing. And then do it so that it supports the song and what everyone else is doing.

General considerations

These aspects actually apply to all instruments, not just keyboards. But since keyboards can sound like anything, it's particularly important to think about fitting together with everyone else.

Fitting together rhythmically: if you play rhythmic comping, make sure that it fits in with how the bass, guitar and drums are comping rhythmically. If you use a sound that has a clear loud attack, you have to think that it's a drum.

Fitting together harmonically: your parts have to be in a pitch range that goes together with the other instruments. And it has to play the right notes so the overall chord makes sense.

Fitting together melodically: if your parts have a melodic element, it has to fit in with the lead vocals and any other melodic lead instrument. Fill in the gaps, don't step over the existing melody. Think about it as "counterpoint".

Fitting together as a texture: if there's a very bright guitar sound, you might want to play something more mellow or dark. If everything else is very thick, play something less thick.

Things to play on keyboards in general

Types of things to do on a keyboard are:

• (1) rhythmic comping. Like guitar strumming, but on a keyboard. This can be (a) two-handed left/right alternation ("stride"), (b) one-hand backbeat like in reggae, (c) chord arpeggios in a steady rhythm. You need to think about what the rhythm pattern is. If your group was a salsa band's rhythm section, which part do you play - conga, timbale, shaker, clave, cowbell? Do you double an existing rhythm part, or play complementary counter-rhythms?
• (2) background pad. You play slow pad sounds which create a harmonic background filling. Either full chords or even just single-note lines. A high legato strings sound that stays as close to some single pitch as possible in a voice-leading sort of way can glue together the whole sound of the group. In a chord progression C, F, Gsus4, G, C, your single-note legato line would play the notes C, C, C, B, C.
• (3) melodic fills. You play countermelodies and "fills". For example with a brass sound or a "heaven/fantasy bell".
• (4) melodic doubling. You double an existing melody and give it more power. Either in unison, or e.g. a third/sixth above or below.
• (5) special effects. Come up with a strange sound and add it sparingly somewhere in a song. It may catch the listener's ear and make the song memorable.
• (6) full piano accompaniment. All of the above at the same time. You play as if there were no other players in the band, and others adjust to your piano playing. This is typically done in slow ballads. It's also a potentially dangerous thing to do, if others don't agree with you taking the whole stage.
• (7) synth solos. Well, not everybody does this at all. You play like a guitar solo, but on a synth. Impress everyone and show off what you can do.

Particular standard keyboard instruments

A lot of the time, a keyboard player can just play "synths" and quite freely select the type of sounds to use and what to do with them. But there are a few specific real physical keyboard instruments with specific commonly known uses and genres that a keyboard player should know about. I would call these standard instruments, and they were widely used by keyboard players before around the 1970s or 1980s, when synthesizers started to be utilized for all kinds of sounds and a keyboard could sound literally like anything. Standard keyboard instruments include:

• The acoustic piano, of course. You should know what sort of things are generally played with acoustic pianos in pop/rock. For pop/rock check out Jerry Lee Lewis, the Beatles, Carole King.
• "Rhodes" i.e. electric pianos such as Fender Rhodes and Wurlizer. Used a lot in soul, r&b and jazz. Check out Feel Like Makin' Love by Bob James (great version by Roberta Flack), or Riders on the Storm by the Doors.
• Clavinet. Check out Superstition by Stevie Wonder.
• The Hammond organ. Electric drawbar organs, usually with "Leslie" rotating speakers and slightly distorted sounds are used in a lot of soul and rock music. This is an art form in itself, and in some bands, there is an organ player that plays a Hammond organ only. But for specific songs, a keyboard player might be tasked to play a Hammond part, because there has to be a Hammond sound in that song. Any other sound would be wrong. Check out Smoke on the Water by Deep Purple, or A Whiter Shade of Pale by Procol Harum.

What's the simplest thing to get started?

The above is already a lot of things to learn. But the good news is, you don't need to do all of that, or even most of that at all. Do one simple thing that supports the band, and you're already adding a significant contribution. The most important thing that's required from any band member is to be a nice person and support others. I recommend starting with the following simple thing: play pads with 1-3 notes and follow the song parts. For example, in a verse, play a single chord tone for every chord, and in a chorus, play three-note chords. For the sound, pick a synth pad or electric piano sound. This is very easy to do, and if you don't play the wrong notes, you'll make a positive contribution. If you can sing backing vocals in the chorus as well, even doubling the lead melody, you'll be a super useful band member.

What does my left hand do? And what does my right hand do?

It depends on which musical element (of the listed 7 things) you're doing. If you're playing synth pads, you only need one hand or one finger. You don't have to use both hands. As a matter of fact, you don't have to play at all! One of the common mistakes that pianists do is when they try to play keyboards, they play too much all the time, "full piano accompaniment" all the way and they never shut up. Don't do that! Do one thing only. Play a tambourine if you absolutely must do something with your hands all the time.