another thing you might try doing at least with the road bike is borrow someone's wind trainer. It's a thing that holds your bike stationary. you could then start practicing with the gears.
Or:
before you get on your bike, check which chain ring you're on.
Put your bike in the middle chain ring in the front. and just leave it there.
Now start riding around again. In the middle chain ring, you should now be able to use your right hand to go through all the gears without getting the chain to come off.
and practice shifting gears now, (right hand) so you can start to feel the differences and know when to use them.

A lot of us started on single speed bikes, and then we got 3 speeds.

to start right off with a fancy 27 speed bike might be pretty overwhelming.
So take it slow and don't run too much before you learn to walk.
I am very impressed that you are learning to ride!