BB press plugin

Hi, this may be a stupid question but, i have just installed the BB press plugin so i can have a forum on my site, the only problem is, it is asking for people to login to post which is what i want, the trouble is, i do not see a feature on the plug for login.

does it mean that my own site already has a login feature.

the problem i have is, i do not want people to be able to get into the site and add or change articles but i do want them to be able to post on the forum.

can anyone explain to me what i need to do please