Hi.
I recently bought some manure for my orange and lemon trees and now there is something growing in the soil.
I am just wondering if anyone knows what it is?
Thank you.

Its some kind of fungus. You don't need to do anything about it, its a sign your soil is healthy

Does look like fungus indeed. There's more than likely no reason to worry about. The majority of fungi growing in/on soil are detrivores (they consume dead/dying organic matter) and pose no threat to your plants unless they are known to act as opportunistic parasites when the chance occurs (aka your plants are already dying/stressed). If your soil and thus your plants are healthy that chance is small.

Don't do anything and let nature take its course. They recycle nutrients and make them available for other life so play a major role in ecosystems.