section targeting on forums and how to use it

i want to use section targeting
to tell google crawler about the contents i want only and ignore the rest using the tags
<!-- google_ad_section_start -->
to highlighting the parts i want Google to focus on on forums how to do it ?

and where to put the tags in my forums to focus on specific forum and ignoring another ?

i use ib board
it will be useful if i can control with ads like that

 

i found this

any additional suggestions ?