You can see how to stick a sticker in a video on the right side.
Before sticking a sticker you need to thoroughly clean and degrease the surface on which you will be sticking, for example by using spirit alcohol or methylated spirit.
It is recommended to stick the stickers in a temperature above +8 degrees and to leave a sticker in this temperature for about 24 hours. The stickers should not be kept before sticking in places with too high temperature, they should not be stuck in the sun, should not be stuck on too hot surfaces. All of this may cause their stretching and also cause serious problems while sticking, it can even permamently damage them.