A birth plan is a document that you create to let your health team know what you would like to happen during the birth, on it you can outline who you want as a birth partner, whether you want no pain relief, or if you’re open to having some /all pain relief offered, whether you want lots of junior medical staff present or not.
You can also outline whether or not you want your partner to cut the umbilical cord, and whether you would like your babies handing to you straight away after the birth (assuming they don’t need special care) or whether you’d like them washing and dressing before you have your first cuddle.
Whilst it can be very useful, I would suggest you make it clear that you might change your mind on the day. Some people think they want no pain relief at all but when the day comes find they want lots of pain relief, which is fine. It should be a guide rather than set in stone! Some people don’t write a birth plan, preferring to play it by ear, it’s entirely up to you.