How can I use System and Bionicle elements together?
since the bionicle-pieces only have holes for technic-connections and no studs to use then directly with bricks, you'll have two possibilities:


build some kind of "adapter" using technic-pieces. you could use pegs to connect the bionicle-piece with some kind of technic-brick.
put the studs of your system-bricks into the bionicle-pieces technic-holes - which may not be the best idea


I'd prefer the first option - it's easy, more robust, not controversial and just need two or three pieces in most cases. for example a brick with axle-hole and a small axle or a brick with hole and a simple peg is all you need to get started.