Once you unlock the bike and have an active rental session, you can lock it anywhere using the cable lock.
The combination code is shown above the name in the app.
Make sure you lock bikes to a public bike racks.
When you want to end the rental session, bring the bike back to the original rack where you found it.
Only the original chain you unlocked the bike from will work to lock it back up. Make sure which chain you unlocked it from.