I am a big hack fan, next to sqauts they are my favorite for building quad size. Since your gym just got a hack machine, is this the first time you have ever done them? If so stick with the basic hack sqaut movement, feet shoulder-width apart, toes pointed slightly out, squat down to 90 degrees and repeat; pretty simple.
One of my favorite variatons is to do wide stance drop sets. This is where I place my feet out towards the edge of the platform so I am at a very wide stance. I then take up to 10 seconds to lower the weight and pop back up at normal speed. I really like these towards the end of qaud day, it really fills them up with blood.
i go a little past 90 but that's me...i do them in the 8-20 rep range after BB squats. i alternate front squats and machine hacks every few weeks.