It should sink down (unlike a soufflÃ©!) as it decomposes, so keep adding material as you have it. After awhile - maybe a month or two, shorter if it heats up, longer if it doesn't - it will be time to turn and mix it. If you can remove the bin from the pile easily, set it down next to the pile and fork the pile back into it. Usually when I do this, by the time fall comes I have compost. At some point you will need to stop adding material, and that's a good time to move your bin off the pile again and start a new batch in the bin. Whatever did not decompose from the last batch, you can toss in there when you harvest the compost.
As you can see, the problem with having a compost bin is that pretty soon you need a second one.