I have loads of hero coming in my inventory but can’t use it. How do I access it?

All the heroes that you have recruited appear in your 'Hero' menu. The button is near the bottom on the right. To use heroes though you need to place then either in your legions (combat heroes) or station then in production roles. Tap on the Town hall building for Stationing.

Any duplicate heroes that you recruit will give you Hero medals. You can see this in the Arena under the Exchange option. These can be used to unlock skills for your heroes or exchanged for wisdom medals.