It takes awhile to get accustomed to a bike, and especially the gears.

~~Most bikes have on the
left handle bars, controls for 2 or 3 chain rings. You may have numbers 1, 2 and 3... or low, mid, and high. The chain rings are located by your pedals. These front gears aren't actually used very much at all. When you first get started biking, you should make a point not to worry about shifting them your front gears at all. Most experienced cyclists will pick one and stay in it probably 90% of the time.~~
If your bike has three chain rings, when you are on 2, the chain should be on the middle ring.
On 1, the chain will be on the smallest, and on 3; the biggest.
So pick 2 or mid, and focus on learning how to use your back gears, the controls on your right handle bar.
The right handle bar: number of will vary. My bike has 6 gears on this shifter, ( and 3 on the left meaning my bike has 6 X 3= 18 gears.)
If I am riding with 2 on the left, and 2 on the right = I am riding in 4th gear, and the pedaling is easy.
If I am riding in 12th gear ( 2 on left and 6 on right) and encounter a hill, I will gear down to 10th gear ( 2 x 5), or less.
If I am biking downslope, I will use my highest gear .. Left 3 x Right 6 = 18.
This is my favorite gear; slow pedaling with much distance, but I try to ride on the middle chain ring for the most part. All around easier.
It takes practice to learn what gear you need where. In time you will find yourself gearing down without even thinking in preparation for the incline. Shifting down while pedaling hard, and it's hard on your bike. Look ahead, and plan.
Gears to avoid: 1 on left and 6 on right and also 3 on left and 1 on right. It's hard on your chain and your sprockets to be at extreme angles.
Don't try to shift when you are stopped. Bikes with traditional gearing are designed to be shifted when the pedals are moving, so don't try to shift when you are stopped. It's bad for the bike to shift when the pedals are not turning.
Gear down before you stop and, and you'll be in the right gear that you want to be to starting out .