Warning: these things are ridiculously fiddly to setup. Top tip: take one of the metal frames out of the box altogether first, leaving you space to setup one inside. Tie the fixed fabric tie first, then use the supplied cable tie to do the other side, then repeat for the other frame.
Both loose frames are for the side walls. Hope this helps save you some time and frustration - it's only a 10 minute job but it should be 2!!