Growing your own cannabis plants starts with a number of seeds, which can mainly be bought cheaply on the internet. Hundreds of different types of cannabis exist, so also just as many types of seeds. You obviously choose a type of which you know you like the weed it produces. Popular types are: White widow, Blue berry, Northern Light and Super skunk.
Also pay good attention that you buy the right cannabis seeds, because some types are more suitable for growing outdoors and others for growing indoors. Seeds of which you know beforehand they are female are also available. These are called feminized.
Cannabis seeds can for example be bought at: Dutch-headshop.com