A bassline is created in the Beat and Bassline editor (BB Editor).
We use bass01.ogg from My Samples sidebar, and drag it to the BB Editor.
We change the track name to Bass. Right now it will still have steps.
We can right-click on the steps and select Open in Piano Roll. We can create a pattern like this:
Note that in above, velocity (volume) of first note and the approximate middle note are reduced. Now the sample will be played at the indicated frequency in time.
The patterns for the Song Editor and BB Editor are shown here:
The resulting audio in Audacity shows how the bassline is rendered.