How strong is my prescription?

No its not very strong at all. In fact, its quite a low prescription for near sightedness. The smallest amount of prescription you can have is -0.25. You have about -0.50 in each eye. This means that it is only a couple of steps in prescription as they go up in 0.25 steps.

Not very strong at all, and probably would not be needed for full time wear. Maybe night time driving or any scenarios where you struggle to see things far away

Edit: yep, you would have been struggling with your vision and noticed a difference if it was really a strong prescription.

All the best

Well, what prompted you to get an eye exam? Did you think you needed them?

You are very mildly nearsighted, and you have a minor correction for astigmatism in your left eye.

So, if you got the eyeglasses they would probably sharpen your vision driving or watching television and if you're a student it would make a difference there too.

The guy at the store made it sound worse than it really is, so he can make the sale or maybe he's just a salesman and doesn't know much about prescriptions.

He was lying to get you to spend more money on a better pair of frames. Your prescription is extremely weak, you'll probably just wear glasses to read the board in school if you're in the back row, that kind of thing. I probably wouldn't have even gotten glasses, unless you have trouble seeing certain things that are necessary.

Right eye -3.00

Left eye -3.25

I have a medium prescription, some people have it way worse.

You barely need glasses. In fact I'd say glasses would be optional for you.