Most of the sheet music you buy will be arranged for piano. Piano music is written using two or three staves, with the chord symbols written above the top staff. It may also contain unfamiliar symbols and terms. At this stage you need only look at the chord symbols to create your own bass lines or look at the bass staff and copy the piano bass line.
Many piano arrangements do not sound anything like the recorded versions and the bass line for a piano arrangement can vary greatly from the actual bass line played by the bass player. Guitar tab and bass tab versions of sheet music are gradually becoming more popular and in many cases are very accurate arrangements of the song.
When you see an unfamiliar chord, consult the following table to find an easier chord to play. This chord will still sound correct. For example, when you see a Cmaj7 symbol, play a C chord arpeggio instead. For a Cm6, you can substitute a Cm chord arpeggio, etc.