Usually, when you go to a website that requires flash, you should be prompted to install it. It should walk you through it pretty easily.
If it doesn't install automatically you can go to the terminal (applications>accessories>terminal) and enter:
That should install all sorts of software, mp3, and video codecs, and of course, Flash. You can just copy and paste that right into the command line. You have to use right click to paste.
sudo apt-get install ubuntu-restricted-extras
PS here's what the prompted method looks like.
PPS As you are new, you should probably get familiar with the methods Ubuntu uses to install software. It's much different than Windows. If you try to install software the way you used to in Windows you could end up in trouble. It's very simple, just different.