Hi
As long as its well rotten you can just scatter on the top of the soil the worms will do the rest for you.

You have to let horse manure compost at least 12 months before you use it. This way you will be assured that it is well cured for free release of nutrients and free of insects and weed seeds. So inquire before getting bagged manure direct from a stable whether it has been composted properly. If it is fresh, place it into your compost heap if you have one and leave it there for a while.

It's also good to know whether the horses have been stable fed or field fed. Field fed manure will likely produce more weed than stable fed. Even well matured manure can still produce weed.

Fresh manure contains too much salt and ammonia which will burn tender plants and the roots. As stated above - let it compost completely before use in garden.