Creating bass accompaniment

I make minus one for my compositions and my problem is the bass. A friend said that what I can use for the bass is the chord of the song. That I play one string in the chord that I prefer. I hope I am doing it correctly.
A lot of guitar players don't need a bass player. As Alexandoy pointed out, they simply use the lower guitar strings for the bass. In other words, they sort of become a one man band, so to speak.

Note, If you ever get the chance, especially check out fingerstyle jazz or classical stuff. It provides a lot of examples.