First start by washing your hands and cleaning you fingernails. You’re going to be going inside your body, so you want to be hygienic. Then, get comfortable, lie down on your bed. Begin to rub your breasts - touch the nipples, if you want. Make your nipples erect - it’s really fun to mess about with erect nipples. Then move down to your thighs, stroke them and get closer and closer to your vagina.
Open the labia lips and stroke the small lump covered by loose skin, called the clitoris, play with it a bit. It really depends on how you like it, so if you like to just softly stroke and circle your clitoris that’s fine or if you like to press down on your clitoris and really play with it that’s fine too.
You should be starting to get really wet now and feeling unbelievably good; wet your fingers with the vaginal juices then move down to the vagina opening (the vagina opening is not the small hole near the clitoris, it is further down). Slide your finger into your vagina and start to move it around, you don’t have to go deep into your vagina, you can just hang about at the opening. Or you can move your finger up and down inside yourself. Whatever you do, enjoy it.
If this is your first time fingering yourself then it is good to explore and see what feels good and what doesn’t.
You could also use a vibrator, try two fingers, lie on your front, etc… You should really try to experiment and don’t feel bad about it afterwards, it’s a natural thing that everyone does.