When I was new to Ubuntu I was overwhelmed like you but don't worry; UNXS there is a ton of resources that you can learn from. Visit these website's; read and learn it will help to do some reading.
Also if you can either purchase this book or borrow it from you local library; do so-
"Ubuntu Linux" By: William Von Hagen
I'll try not to use technical talk but that's the challenge I took on to help you.
When you first turn on your computer it should show you which # or version of Ubuntu is booting.
You say that your OS is "constantly freezing"
Please try to give a description of when it freezes and what you seem to be doing just before the freeze.
Right after boot up? Or as soon as you go online? As soon as you run a program or application?
Finding out what graphics card won't be hard at all. In order to find out which one you have you will have to find your "Terminal" Look up in your Applications menu ->Hover over to Accessories -> Scroll down to "Terminal."
When the terminal opens you should be greeted with something like (just an example: Debianuser@sid$)
At that prompt right after the "$" sign type in the letters:
And press Enter. Copy and paste all of that text that you got from the result of 'lspci' and post it back here on the forum so one of us can help to diagnose your computer and find out what graphics card you have.
Take your time to learn what you can about Ubuntu. You'll get there just like the rest of us did