@Johannian Technically, all you really need to do is add pollen from one flower onto the stigma of another flower, label the cross (if you care to know what the parent plants were), collect the seed and grow out the new plants (called the F1 generation).
I guess the bigger question would be what are you hoping to accomplish? If you are hoping to create a new variety that people would want to buy then it's a whole lot more complicated!
