Try an electric razor first. It doesn’t give the closest shave but it is much more difficult to hurt yourself.
If you don’t have access to an electric shaver use a disposable razor with shaving cream and rinse the blade often. Don’t try to shave with a dull razor or when hair is clogging it. If your leg hair is long you may need two disposable razors to shave your legs the first time.
Go slow, do this when you have plenty of time. Rushing leads to nicks.
You will nick yourself occasionally and that is ok. Don’t panic and put a bandaid on.
Try shaving your underarms and lower legs first. Shaving the public area, if you decide to do so, is an advanced skill and you should wait until you feel more comfortable with shaving.