Two... no three... methods spring to my mind....
Using two stout sticks and some good lengths of cord - you could either -
- Tie the sticks into a "X", suspend the centre of the cross from a branch and hang the canvas a few feet under it (like an upside-down parachute), then you sit in the pocket of canvas.
Or
- Hang the canvas like a small hammock and use the sticks as spreader bars at either end - you might get a bit of back-support as well this way!
Or
..... use it like a First Nation Indian chair - find an inverted "V" shaped branch that you tie one corner of the square to the top, then tie the next two corners around the back, you sit on the remaining corner and lean it against a tree.
ATB
Ogri the trog