In reply to hannahbannana:
1) Tie both ends of the rope to your harness
2) Place a piece of gear (or several!) and clip to the massive loop you've created
3) Climb. Try not to fall off or you'll go until the loop comes tight on the gear!
4) When the loop comes tight untie one end and pull through - abandoning the anchor lower down.
There are tricks for keeping the loop only as long as you need as well. In general you REALLY don't wanna fall belaying like this...