Re: total n00b question…
After activating the plugin I would do 2 things.
1. go to admin-settings-forums (in the admin panel) and click save.
2. go to admin-settings-permalinks (in the admin panel) and click save.
The reason for those steps, although probably unnecessary, is to set the permalinks for everything. Like I said, probably not needed, but can’t hurt.
Then if you didn’t change anything on the forums settings, you can go to mysite.com/forums/ and there they are.
*Next you may want to add a link to the forums in your website navigation so that people can find them.