You need to place an object...

How do you choose which skill to assign to it? :rolleyes:

Unfortunately, unlike the editor for the third game, this cannot be done; it's completely random. :(
Usually, to set certain parameters for an object, you need to select it on the map and press Object Properties (the 11th button from the left) or the Spacebar key. But this can only be done with certain objects, not all of them. For example, you can do it with a Ruined Mine or a Garrison, but not with a Witch Hut. :)