Beginner's Handbook to DFO

Just a couple questions:

What are pets used for, exactly? Are they used to buff yourself, add stats, add extra attacks...?

I also sometimes see blue numbers jump out after hitting some monsters, and was wondering what those were.

Edit: One more...

I made a WM, and have no idea what weapon mastery to take. I'm guessing it would be smarter to wait until I can get a decent weapon before I pump points in?

in order of asking:

Pretty much just that.

I have no idea what the blue numbers are for.

Most people go with lightsabers, though you can choose whatever weapon you want. If you're just beginning, you may want to take a look at a few WM builds before making your own.