MyBB Community Forums

can i use one domain name for home page and a forum?

1) Why is this a poll?
2) You could put your main website in your main website root folder (/html, or whatever it is on your webhost), and throw MyBB in a /forum subfolder.

Like that 

Yes, that's the correct way to do it. If I were you, I'd lowercase "Forum," as folders in the URL are case sensitive.

now i put "My URL"/Forum

now?

Yep. That is correct.

Do u have a skype My is not working

Your forum directory needs to be under the public_html directory. Anything that isn't under the public_html directory is not accessible on the web.

Like that? 

^ yes, like that. forum folder consists of MyBB files