These are some options you have will Logic Pro.
I'm assuming that by keyboard you are referring to a qwerty keyboard and not a MIDI control surface.
Use your qwerty keyboard as a control surface
Activate your qwerty keyboard as control surface by toggling caps lock on. This image will appear, indicating that your qwerty keyboard is now functioning as MIDI control surface:
In Logic X a different image will appear, but the concept is the same: Musical Typing.
Now your qwerty keyboard works more or less like a piano keyboard. As you can see in the image, a = C, w = C#, s = D, and so on. You can control velocity with z to m. z = pianissimo, p = piano, and so on. You can switch octaves with the numbers.
Now enable record in your midi track (create one if you haven't) and start recording. Every input note will be recorded.
Score Editor Chord Grid
You can use the Chord Grid inside the Part Box, which is inside the Score Editor, to input chords as guitar chords.
Step Input Keyboard
You can use Musical Typing (your keyboard), or a on-screen piano keyboard, to input notes and chords step by step.
Logic X instructions
Logic 9 instructions
There are many ways to input musical information in Logic. For me the most practical, without a MIDI control surface, is to input the notes in the Piano Roll using the pencil tool.
I haven't found something that matches a control surface, like a MIDI piano keyboard; fast, simple, familiar, multiple attributes input at once (velocity, aftertouch, note), etc. You might want to consider acquiring one.