Yo, Alex.
In order to make a singleplayer map, just make a simple map, I mean, with the map sections, then put player map positions and it's ready.
If you're trying to put units into the map, even New Era ones, it'll work like it is a mission map (campaign map). It means that you're making a Scripted map, u know? Like, if you put a swordsman for player 1 to start with, that's a scripted map ("mission map"). Those are harder to deal with, as Scripted maps are playable only in multiplayer, but with my tutorial you'll be able to play them in singleplayer (after you made it): https://www.youtube.com/watch?v=qrr-zSZR8gE
Btw, you can add New Era units into your map by putting "The New Era Mod.hpi" file into your TA:K directory (C:\Cavedog\Kingdoms, just like if you have installed it, then the units will be available to be used in your map. ^^
If you have any question, ask here, I can make it clearer if you want. xD