youve never had a suit before?

generally speaking, you go by the chest size like 42 or 44 or 46 and so on. then you pick L, R, S, for long, regular, short. pants, are regular pants sizes by the waist.

best thing to do is however to get it all tailored to fit your body. but if youre in a rush and/or dont care then you can just get the "pre-fitted" ones.