Chicken manure pellets are usually made of the spent bedding, poop, feathers and anything else scooped up in the clean out. They mainly provide nitrogen, which is great for green leafy growth. There is some phosphorus and potassium, but not as much as other fertilisers sold as general fertilisers.
Having said that, they are good for a lot of stuff and if they have been given to you free, that is a bonus. The only thing I know they are not so good for is ericaceous plants (blueberries, rhododendrons and the like). They are generally fairly alkaline, so don’t suit acid loving plants.