On my next vacation, I will be camping in a tent on a designated campsite. I saw somebody use a hammock for lounging during the day last time, so quickly got a cheap hammock from eBay, with a "let's see if that works for me" attitude. 

The hammock came, and it is a piece of silk with a spread of ropes on each short end. The ropes are braided together into a loop. I think this might be intended for a specialized hammock stand, but I won't have one, I'm hoping there will be a usable pair of trees in or around the campsite. It is roughly this style: 

![hammock type](https://i.stack.imgur.com/vQOLu.jpg)

How do I attach it to the trees? Can I use any old cord and wrap it around a tree trunk? Won't it slide down? What cord thickness do I need? Are there special knots I should learn? Is there something more convenient than a cord, e.g. some kind of short belt with clasp? (I've seen long ones for fastening kayaks to car roofs, for example). If I want to buy something for this purpose, 1) how is it called, 2) which shop has it, and 3) how do I use it?