In Bookinglayer we make a difference between Bookers and Guests. A booker is the person who makes the booking. A Guest is somebody who stays in your camp/retreat.
For Guests you can store fields like Phone number, Level, Diet, Date of birth and Language, among others.
For Bookers you can store address info (and e.g. a Tax Number for clients that book as a company).
In 99% of the cases your booker is probably also participating so he/she has both a Booker and a Guest entry in Bookinglayer.
Remember that you can create custom fields for each guests or bookers. Please refer to this article.