You can now follow the chords of almost any song in the catalog. Go to Songs and find one you actually want to play.
Start on roots. Add eighth notes if it wants more push. Add a walk where a line ends. If a chord has a # or a b, you can find it from the notes you know: one fret up is a sharp, and one fret down is a flat. Three flats sit on open strings, so use these: Eb is D string, 1st fret. Ab is E string, 4th fret. Db is A string, 4th fret.
Bass is a team sport
More than any other instrument here, bass makes sense when it is with something else. Playing with a record is a good start. Playing with one other person is better: a friend on guitar, or anyone with a drum machine or a drum app. Stay on the roots, and listen for their beat.
If nobody is around, press Record a clip on a song page and listen back. Are your notes starting right on the beat, or a little behind it? That is the first thing to hear.
You're done when: you have played a whole song with another person, or sent someone a clip of you playing.