I can write a quick how-to guide:
(assuming you already got the correct path settings all set)
In the main screen "Map Editor", you can browse the different maps.
First you make a backup of the MAP file (in the MAPS subfolder if your game) that you want to change.
Click the map you want to change, don't look at the RMPview for now, first we use the TopView and TileView.
In the topview click the cell you want to change. Then click either ground, West, North or Content. Then in the TileView screen, click the corresponding tab with either ground, walls or objects. Then right-click on the sprite you want to place there.
Repeat this for all cells you want to change. Et voila - your map is done.
Now go to the RMP view. This is a bit harder to understand, because it's more behind the scenes stuff.
Ideally, you don't have to edit this. But you might want to check if the nodes are not in places where they cause an issue if a unit would spawn there. (for example on an object)
If that is the case, then you first rightclick on a cell, this will add spawnpoint/patrol-node. Then you fill-in all the data of the original node to this new one, setting by setting. Then you delete the old node.
