I haven't hit my period yet and I want to start masturbating

Start by rubbing your vaginal area. gently spread the lips of your vagina and rub gently up and down and in circles, you should soon begin to feel good and maybe even get a little wet (Fluid will come out from the vaginal entrance). Keep going with what ever feels good. Once you are wet, you may want to insert a finger inside your vagina and begin stroking it in and out as well as rubbing your clit and outer vaginal lips.
There is no harm in masturbating, just relax and enjoy. May take few time before you find what makes you feel really good.