Current questions and answers regarding the map editor.

No, DDS doesn't read that format. There isn't one at all. It's either TGA or PSD. Neither worked. Maybe I'm doing something wrong?

DDS, that's correct, as Ment said.
By default, Photoshop doesn't know how to save in that format.
Therefore, for DDS, if you are using Photoshop, you need a special plugin (Google can help you find the plugin, because I don't remember the link).

Added after 8 minutes

And how do I make it so that, for example, in the Seer's Hut, the player gets 1000 gold for 20 sulfur?

With scripts.
We attach a trigger to the building. (An event happens when entering it)
In the trigger execution function, we write the code to receive gold for sulfur.
(if GetPlayerRe.... == 20 then SetPlayerR....(GetPlayerRes...(Player_id,(gold)+1000))
If it's not clear, then study the script alphabet ;)
You can learn it in the Manuals, on this and many other forums, using the internal search, and if you need specific details, then you just have to wait for our forum's "Archivist" ;)