There are many ways of hanging a hammock, this post describes how to use whoppies. Other posts describe how to use a farrimond hitch and a pair of rings. The first thing to do is to lash to the tree. Prefer thicker rope or webbing over para-cord to avoid damaging the tree. Tree straps can be made from 3/4 inch wide polypropylene webbing or purchased here.
As an alternative to using an adjustable tension knot, whoopie’s work amazingly well. These work a bit like Chinese finger cufflinks. The cord has been braided in such a way that the cord loops and passes through itself. Under tension, the outer cord squeezes tight against the inner cord. Whoopies are lighter weight compared to a pair of rings but have fewer uses. It is also very difficult to loosen them when they are unfair tension.