In recrystallization the idea is to suspend the product in a few mL of a solvent and then heat it in order to obtain a saturated solution at the boiling point from which the product crystallize while the solution is cooled, impurities stays in solution because the solution is diluted in regard to them. You need to find the right solvent that is one in which the product has a low solubility at room temperature but a high solubility at the boiling point. Water won't work beacuse solubility is too low, ethanol ora acetone won't work because solubility is too high. If you find the right solvent you'll need to suspend crack with your solvent in a flask and heat it on an electric burner (no flame) then at the boiling point you eventually add more solvent in order to dissolve all the crack and stop the heating and put the flask in ice, then you can scratch the flask with a glass stir to help the crystallization. To not let the solvent evaporate put a funnel with a filter in it at the top of the flask. You can also use a second solvent in which the product is insoluble and add some drop of it to the solution while is cooling, until you see that the precipitate won't redissolve anymore, that is a two solvent crystallization.