Understanding what your birth plan is can be a great help to your support people and care providers. It provides them with a reference to how you wish to labour and birth your baby without them having to disrupt you and ask questions. And if you have this all written down, your care providers are more considerate about your care.
Things such as how you want to labour (water, active positions, where, etc.), how best to manage pain of labour, routine vaginal examinations, augmentation of labour and rupture of membranes, cord treatment after birth, third stage (delivery of placenta), going past your due date, and so much more.
Most hospitals I have supported women to birth in have similar guidelines and processes, and if you know how the hospital system works, you can plan to negotiate some of these protocols before you birth. This is especially important if you are choosing to really go outside the box and have a Lotus Birth, or physiological third stage, or resist being induced for example.
A birth plan is not going to guarantee a pain free intervention free birth, but it will guarantee that your care providers are extremely well informed about what you do and don't want - and "informed consent" is a very important term in the birth room.
Be proactive and take control of your birth choices, with the help of a birth plan.. You can create a birth plan yourself, get onto your computer and google a couple as examples.