The guitar and bass are another very important part to a band. The guitars  play  melodies and sometimes harmonies. A guitar consists of 6 or 12 strings, and anywhere from 22 to 26 frets. The bass is tuned an octave lower, and has 4, 5, or 6 strings. The strings on a bass are the bottom 4 strings on a guitar, E, A, D, G, just tuned a lot thicker and tuned a lot lower. The bass keeps the rhythm, often following the same rhythm  as the drums.
This is a classic beginners guitar. Fender Squire is an awesome guitar for a newcomer in the world of music because it has a good quality for what you pay. Squires are a good buy, because for the small price you pay, the quality and sound of the guitar is very nice.
 

For a guitar like this your going to spend anywhere from $700 to $1300. Lenny Kravits uses this guitar. Some say Gibsons are a rip off for the price you pay the the quality you get. Some have the exact opposite.
This is an acoustic guitar. Acoustics don't need and amplifier. An acoustic is a hollow bodied guitar that catches the sound and amplifies it naturally.
This is a bass. A bass is tuned an octive lower than a regular guitar and consists of the 4 bottom strings of the guitar.