What is the right size for a signature? please tell meh :3

I believe 450X100

Thats the tp size.
If you have VIP its 500x200.

Question no2: how do i put my "picture" into the signature ? (i suck with computers)

After first buying Toriprime, simply go to this page.
There's a section called signature picture there. You can either enter an image Url if it's already uploaded somewhere or you can upload a pic from your computer.
Then in the signature editor, place these tags where you want the sig pic to be.
[SIGPIC][/SIGPIC]
You'll probably need to do a few previews to get it right.

Actually the VIP size is 650x200...