How/where to look behind me while driving to get over to other lane?

I'm 16 with my permit and new to driving and I'm having a lot of trouble seeing when i merge to the lane in the left of me. My mom yells at me because i slow down a little and try to see and she tells me "quick looks" but I can't really see when I turn my head. I drive a honda civic. I don't know if am too short (i'm almost 5'2'') but I don't think thats it. Should I look out the back window or side window in the backseat? I try to use my mirrors as well but I just have difficulty knowing if I should go or not, please help me thank you. I don't want to never be able to drive

There's only one small blind spot that you can't see from your mirrors

So check your mirrors first. If you see a car in them, then obviously it's not safe to change. Then you just need to glance over your shoulder and see if there's a car beside and slightly behind you. That's the spot your mirrors don't show. You don't need to stare out the window, just a check that there's nothing there.

Also, slowing down to change lanes is a bad idea. That means cars are going to be coming up INTO that blind spot. If you go slightly faster, you can see the cars ahead easily, and judge your gaps better.

If you have a good view out the rear mirror (no luggage or footballers blocking the view) adjust your driver mirror so it complements the interior mirror view not duplicates it.
rear mirror, side mirror, shoulder check, then again to see what changed. Check for motorbikes and cars moving faster than the flow.

some cities, you signal and move then people will get out of the way but not before. Others, you signal and wait for a gap. So you have to behave how other drivers expect.

even if your mom yells at you, you're still in charge and you should not move if you know it's not safe

Quickly glance over shoulder through rear side window. You look at rear view mirror to look through the rear window, you glance at the passenger side mirror to look down the passenger side of the car, and back through the passenger rear window again, to ensure you can move right.

You look rear mirror, to your driver side mirror and glance to your left, repeat the cycle and then move right.

All those moves happen several times per second. You should know what the cars behind you are doing as you're driving, so that you know where they are, before you need to change lanes.