Mimi,
I had to get used to my numberless bar end shifters as well.
My only advice to you might be to stay in the middle ring up front while you keep changing the only rear gears back and forth to get used to the feel of those. (needless to say, don't attempt steep hills while you do this).
Once that all becomes really familiar, try staying in a middle-ish gear in the back while you ride around switching between the front middle and small(uphill)gear. Forget the front big gear for now, you can get to know that one later.

These two exercises might help you get a better feel of the gearing, as they did for me.