Hello, Just a quick question

Hey guys, first post i think. i have been using XenForo for almost a year now and im now doing major updates to my website.

I need to remove the register system because im going to merge it into one (my register system)
I need the Session tags from the XenForo forums so when they log into my system it will log them into the forums as well.

I'm not asking for a HUGE guide, just point me in the right direction and ill take it from there, Thanks guys :).