Hammock
A gathered-end hammock in 3.2 m of cord and an afternoon.
An afternoon, 3.2 m of cord
A gathered-end hammock is the classic first project — it uses one knot (the sheet bend) and one splice, and it will outlast the tree you hang it from.
What you need
cord 3.2 m of 6 mm accessory cord knots sheet bend, half hitch tools scissors + a lighter to whip the ends
The build
Gather each end with a sheet bend, whip the tails, and hang it from two trees with a simple loop. Ten minutes of fiddling to get the sag right, then you're done.