This is a really wide open question! 6max opening ranges are obv loads wider which means 3bet ranges also widen, imo stealing/restealing/cbetting really needs to be understood well as the blinds whip round so you need to start playing the person more so than in FR.
If your a fr player at the min then 6max can seem quite daunting, I've made the move myself, but its more rewarding once you get it down and can hold your own.
Google Ryan fees 6max guide for a top guide on 6max play and ranges, it helped me tons, and contribute more to the ha thread as this forum is full of good 6max players who really really know their shit!