Need help with css Boxes (borders)

Hello,

I need your help people.

I want the content of each post to be inside a box(or a border, i don’t know how you call it) just like this one —>
https://img155.imageshack.us/img155/2896/dedmh.jpg
And i want more than one “boxes” in each post.

How do i do that?
I guess it’s a html & css code…but where exactly should i add it?

Another good example is imdb style https://img535.imageshack.us/img535/4025/42617437.jpg

Please help me out.