aggrocrag says:
I don't really understand why there are markings that are not on the fret board
Do you mean the yellow circles, yellow circles with R in them, and the red X's that are off the left end of the fretboard, right beside the:
E
B
G
D
A
E
If so... a yellow circle there means that the string is played "open".. that is, you play that string without freting it.
The red X means that the string is not played at all. If the string that is not to be played occurrs either above or below any other strings you are fretting, then you try to not play it by simply missing it with your pick...
but sometimes a red X will be for a string that is in between two other strings that you are fretting. In that case, you have to "mute" the string. Do mute the string, you have to use one of the fingers that your using to fret an adjacent string and gently touch the string that is not to be played as well...so that the string doesn't ring out when strummed, and just emmitts a dull clunk sound.
This is something that you would understand in a milisecond if someone was showing you in person, but its a little hard to describe in writting.
A few basic lessons would probably get you off to a good start... failing that, try buying an introductory guitar book that has a DVD.
Good luck.