Once you have opened a map, you can start to shape and modify it. You can do the following actions with your mouse:
To select an object, left click on it. You can do so either on the map window or in the map-archpanel window to the right. If you want to select a group of squares on the map (e.g. for copy/paste actions), left click and drag. You will notice a rectangular area getting highlighted as you drag.
To insert a new object, you must first select one of the arches from the default-archpanel to the left. Right click to insert the selected arch into the map. You can also right-click into the map-archpanel in order to insert the object at a specific place in a pile of objects. You can drag the mouse on the map view in order to insert the same arch on many squares.
To delete an object, simply middle click on it. You can drag the mouse to
delete multiple objects. Deleting specific objects out of a stack is
possible by middle-clicking in the map-archpanel.
(If your mouse has no middle-button you can simulate it by pressing
<Strg>+<any mouse button>.)
There is a convenience function for inserting walls into a map: The
"auto joining"-feature. Activate the checkbox in the menu "Map->Auto-Joining"
to enable it. Whenever you insert or delete a wall now, any walls of the same
type will automatically join to form a continuous solid wall.
This saves you the hassle of switching between all the different wall-arches.
If using any arch set other than the standard one, you might need to customize
the file "autojoin.txt" in order to have the autojoining feature work for
all the available wall-styles.