Learn the notes on your bass. You can buy a chart that shows you the names of the neck of your guitar. The strings on a base, from thinnest to thickest, are GDAE. These are the same notes as the lowest (thickest) strings on a guitar, except that they are lower in pitch. You can also find a chart online that shows you the note names of your base (see Resources).
Buy a bass guitar chord list from a music store or use one of the many free bass chord references online (see Resources). Every chord that a guitarist can play with the four lowest strings can be played on a bass. That means you can use a guitar chord in a pinch.
Remember chord forms rather than trying to learn each chord in each key. Learning these patterns and knowing the note positions on the neck of your bass will open up a world of chords with a minimum of memorization and effort. You can move these few chord shapes anywhere on your bass and play another chord without having to change the pattern.
Tips and warnings
Although the bass guitar is usually played one note at a time, bassists can play chords in the same way as the guitarist does. Playing chords on a bass can add depth to the music by creating a ‘fuller’ sound. However, it can be more difficult to play chords on a guitar, as the bass strings are thicker and further apart.