PG (propylene glycol) is a thinner tasteless liquid used to cut the liquid nicotine, PG will give you more of a throat hit when vaping and tends to be tastier to some people but produces less vapor (little harsher) your e-liquid with be thinner with this
VG (vegetable glycerine) is a thicker sweeter tasting liquid used to cut the liquid nicotine, VG will produce clouds of vapor with less throat hit(smoother) your e-liquid will be thicker with this
the effects of these two are diff from person to person, some people dont like VG and some people dont like PG, some people like more VG than PG in their mix and some people like more PG than VG in their mix, or some like a 50/50 mix ratio.... my personal preference is 100% VG but thats my personal opinion, this is something that comes down to your personal liking, and the easiest way to figure out what you like is order 2 of the same flavors one with VG and one with PG then test them both... if you like one more than the other than you can mix the 2 together and see if the same results or if you are completely happy with one 100% of PG or VG then you know what you will like

i hope this helps