Adsense on forums ?

Hi,
I am new here and to the advertisements on the web too.
However, I like to give it a go.
I would like to have some views about adding a forum to my site, and put the Goggle advertisements on it.
I have seen many of these.
The main question:
Where to get forums, what allows to insert the google code ?
Exist some free ?
Or need to be in the "business" category ad pay for it some hundreds of dollars ,
Thanks in advance for all contribution
Attila

Original post by attilaaa