Getting to grips with gears???

[Pat "5mph"]

Hi Jessie and welcome!
All the advice above is spot on, some practice and you will soon get the hang of it.
Don't be like me, I'm sooo lazy in changing gears, that when I get round to do it it's time to change again. I'm always in the wrong gear

 

[Cubist]

Another easy way to remember is to think that the right hand gear lever uses your thumb to change to an easier (lower) gear, and your finger to pull the release lever to change to a faster heavier gear. If you need an easier gear, push with your thumb until it won't shift anymore, then you've run out of gears for that front chainring. It's the opposite on your left hand. You push with your thumb to change to the bigger chainring for a faster heavier gear, and pull with your finger for an easier lower gear.