the gear shifter on the left side (sitting on the saddle) is for your front chainrings 2 or three, if you have them and this is the side that determines how easy (smallest ring) or hard (largest ring) it is to pedal. The right side is 1-8 and these are the cogs in the cassette that determine how hard or easy it is to pedal within the range that you choose on the front. The largest ring in the rear is #1 and the easiest and the smallest ring in the rear is #8 and the hardest to pedal in.... You will figure out which one you need to be in as you use them more and when you need to climb a hill, you will likely be in 1 in the front and 1-4 in the back and on flat roads 2 or 3:front and 6-8 in the rear and so on .....you will get the feel for it you just have to use them. Do not try to turn the grip shifter past its limit as you may damage them and eventually the cable in the shifters will stretch and you will need to have them adjusted, usually after about 30 hours of ridding or so. This should have been discussed if you purchased this bike at a reputable dealer!