I play piano and guitar. It looks like there are talented people that improvise in some way that they play in a really different scale than the main scale they were playing on from the start, but after, the original scale remains. I just know Major scales. I and I also know some other scales but don't know when to use them. I want to enlarge my knowledge, so I already thank you guys for your help.
I understand your plight of knowing the scales but not exactly knowing how to implement them into your playing. First, I'll say don't expect the practice to yield results over night. The scales will have to be almost second nature before you start to utilize them in practical playing. The best advise I can give (based on experience) is to start out simple, but focus more on the SOUND of the scale. Of course, you should be very comfortable with the "shapes" and notes so that you aren't thinking about what note to play next which will then free your mind to really start to listening to the sound. This was an eye opener for me when I was working with the dorian scale (2nd mode of the major scale). If you are familiar playing over a minor chord - which I was - the dorian scale should come pretty naturally as soon as you get the sound of that major 6 interval in your ear (e.g. over Am7, playing A - F#, as opposed to A-F which you find in the natural minor). Using your ears will really help with scalular playing. As Charlie Parker was known to have said, and I paraphrase: "Learn it. Then FORGET it!"
Assuming you can play all the scales I mentioned, you're nearly there. Let's say you want to play some blues. Listen to some blues players, and you'll realise that the notes they play are from blues scales. Work out what key they're in, and try to pick up the actual notes they use, parrot fashion. Shouldn't be too difficult, given that you know which notes would be available to them in a given key. Be aware that some players use three different sets of notes - for instance, blues in A would mean they use A blues scale notes over A, then change to D blues notes over D, etc.
This is a fairly simplified version of what you would do, but it seems to be a good place to start. If it's jazz, then complications roll in, as the chords and keys may change more often and drastically. Country is often quite static and would give a good start for you, often using pent. majors.
A better question would be: What's the supporting structure for the current harmonic function? Which substructures are contained in this main structure?
For example if I see a Cmaj7#11, I automatically associate the function with a Lydian sound, but there are many other scales (structures) that have the maj7#11 as their main chord, and all these scales are also available for you to improvise over the Cmaj7#11.
Also which are substructures of the Lydian? (or any of the others) For example the Minor Pentatonic a half step bellow the root of the Lydian is a substructure. So on a Cmaj7#11 the B minor Pentatonic is a great scale (structure) to use for improvisation
Here's a cool video explaining extacly this example