Notes are given a letter name from A to G, then repeat. A ledger is the five lines that music is written on. So if you count the five lines from the bottom up, the second one is G (in treble clef, that symbol that looks a bit like an &). After that the notes repeat, so the space above that is A, the line above that is B, etc. The device most people use to remember the notes corresponding to the spaces and lines is, starting at the bottom for spaces spells "FACE" or F-A-C-E. So if you're looking at the five lines, the ledger, the spaces between the line going up correspond to the notes F, A, C, and E in that order.
The lines use the device "Every Good Boy Does Fine, or E G B D F.
On a piano you can find G between the first and second black key in any set of three black keys. (if you look at a piano you'll notice a pattern of three black keys, a space, and then two black keys. This can be confusing, but space between B and C is a half step as well as between E and F. A half step is indicated otherwise by the # and b symbol, moving to the black keys, but remembering that doesn't really come into play until you've got the hang of everything else.)