And if so, can it be used instead of poly cement, or are they used to glue different different things?
Liquid poly is very liquid, it's useful for brushing onto large, flat surfaces or for very, very tiny parts, but generally normal poly cement is the thing to use. Never squeeze the tube! If you have to squeeze it means the nozzle is blocked; unblock the nozzle with a pin and hold the tube downward with the the the tiniest amount of pressure until the glue starts to flow. If you squeeze, there will be a 1 minute delay but then it'll come pouring out. Don't use poly cement unless you are sure you want a permanent weld; if you want a bond that can be broken apart (useful when you notice an error) use superglue or a hybrid epoxy. I use Zap-A-Gap quite a lot.
