Gear selection doesn't need to be complicated.
If your roads are mostly flat, and you'll be riding fairly fast, use the biggest chain ring in the front. For mixed flat and smaller hills, use the middle chain ring. The smallest one is for steeper hills. Of course, you can shift to a different chain ring anytime, too.
Then just shift up or down on the back cogs until you are pedaling fairly fast, and not pushing hard on the pedals. You'll soon get a feel for a good gear.
If you keep shifting to an easier gear and run out of shifts, move the front chain ring to the next smallest size.
Once you have some practice, on a quiet road, count the right foot revolutions for 15 seconds and multiply by 4. This is your cadence in revolutions per minute. Most riders do best at 80 rpm or a bit more.