Writing out rock songs as chords is a form of shorthand. It's possible to write every note for every player, but it's not a good idea, for several reasons.
- it's a lot of work
- most rock musicians can't (or won't) read written music with that level of detail
- what really matters is the groove, or feel, which can't be expressed in music notation
- as soon as the musicians understand the song, they know better than you do what notes they should play
You might have heard this conventional definition of a chord: three or more notes played simultaneously. This is sort of right, but not quite. A chord is defined as a set of notes, but those notes might not all be played simultaneously. Some of the notes might not be played at all in a given time slice. And there usually are other notes heard in the same time slice that are not part of the chord. The chord is an abstraction, a flavor of sound.
Each chord's name, or definition, has three components:
- root: the "most important" note in the chord, this note appears first in the chord name.
- bass: the low note. This is usually the same as the root, and if a bass note isn't specified, you assume that the root note is also the bass note.
- type (or suffix): a code that tells you what other notes appear in the chord. If there is no suffix, then the chord is a major chord.
To take another example, G7/B has a root of G, a bass note of B, and a suffix 7, which indicates a "dominant seventh" or "common seventh" chord, containing, in this case, the notes B, G, D, and F.
There are literally dozens of chord suffixes, too many to cover here. As is so often the case, Wikipedia is your best source for further information: http://en.wikipedia.org/wiki/Chord_notation.
Tuesday is Beastly Fundamentals Day.