Both are used for making niquid.
VG is thicker, slightly sweet and makes tons of vapor. It can also make the
juice smoother, but it can mute the taste.
PG is thinner and harsher than VG. It carries flavor better, but doesn't produce as much vapor.
Most people use these in a combination depending on what they want. More VG = more vapor. PG = more flavor and
throat hit.
I use either 60PG/40VG or 50/50 mixes.