If you have only one bin and keep adding stuff to it, it won't all ever get to "done" and you have to do what you can to separate out the oldest stuff.
A 3 bin compost system lets you put new stuff in one bin, start on the next when the first is full, and again with the third. The first should be ready to use by the time you fill the third (if not before) so you have an empty bin again. There are other ways to use a 3 bin system, but this is the basic concept. If you have a lot of stuff, you can have more bins. Just remember when making them that if you are standing there with a 3 tine pitch fork (much easier than a shovel) to turn the contents, you don't want the bins too big. Three "ganged" (where the sides of bin 2 have a common side with one side of bin 1 & 3) 3'x3'x3' bins is pretty standard. I found one with Google where a guy made 4 bins from concrete blocks, 4'x8'. But he cheats, he is an excavator and uses the machine to turn the stuff in the bins
In any case, you want to put some "done" stuff in the "new" bin to help get it started. Toss in the chickens' contribution from the coop as well.
You can't use chicken manure directly in the garden, it has too much ammonia and will "burn" the plants, killing them. However, it is not a problem if they naturally spread some if it themselves as they forage, assuming they aren't in a small area.
Bruce