Need Help

So I was recently given control over my volunteer organizations website after our last webmaster did not follow instructions or help with development.

I’m having some difficulty adjusting to using WordPress, I need to add a Members only forums for the organizations members. the rest of the page needs to be free and open to the public. I will manually add the users in with their emails and assign a generic password that they later can change. I only want them to be able to log into the webpage and not wordpress.

this is the website http://mnemshonorguard.org/

Im no good at code reading or changing.

I tried using BBPress but wasn’t getting anywhere at all. looking for help the correct application and step by step guide if at all possible

Many Thanks