MyBB Newbie Help

Hello to everyone,
I recently purchased my first site, and create a forum for it. Thing is before I buy some premium themes, I wanted to tryout the ripped version of the majestic (which is pretty good theme),
but I literally have no knowledge about mybb forums, so I am here to give a shot. I checked the site content but couldn't find a answer to my solution. If you guys(and gals) help me that would be terrific,
so my questions are simple really (I dont even know this is the good place to post this thread but forgive my mistake if it's not) :
1) How can I edit my theme?(if we talk about majestic 1.8 theme for example, how can I edit logo, links, translate some of the buttons to my original language and so on)
2) What's the "must" plugins for fast and productive forum?
3) And really any kind of information about mybb .. since I would love to hear anything and try to learn.
I would put more questions if I counter them so thank you for all of your answers .