Part 2: Basic Building
Now that we have created a new, empty map, we can begin actually creating stuff. SLADE has multiple tools to help build map architecture easily.
First up, let's draw a simple square room using the line draw feature. This is what you will use to do the bulk of the map building. Line drawing can be started in any edit mode, and the default key to begin line drawing is Space.
Press Space to begin line drawing - you should see a green dot underneath the cursor, and some help text in the upper right corner of the screen. Left click will place a point - now draw 4 points in a clockwise direction, each one 128 units apart (the length of the lines being drawn will be shown in green text), as shown below:
And that's it, we have our first room.
Of course, there is a simpler way to draw a square room, and that is the shape draw feature. Rather than drawing each individual line as before, you draw a shape by clicking the diagonal corners of the shape. By default, you can begin shape drawing by pressing Shift+Space.
Now we will add another square 'room' adjacent to the one we created previously using line draw. Press Shift+Space to begin shape drawing - similarly to line drawing, a green dot will appear underneath the cursor. Help text will appear in the top right corner of the screen, as well as some options for shape drawing along the bottom of the screen.
With shape drawing active, move the mouse cursor and green dot to the top right corner of the existing room and left click, then move the cursor down and right so that the new 'room' is 128x128 units in size, as shown below:
So now we have two conjoined squares making up a rectangular room. Rectangles aren't the only shapes you can draw with the shape drawing feature, you can also draw ellipses (or circles). You can change the shape to draw by selecting it in the Shape dropdown menu in the options bar that pops up while you are shape drawing.
At the time of writing, there are currently only two different shapes to draw with shape drawing. More shapes will likely come in future versions of SLADE.
Next we will draw a circle within the square on the right. Press Shift+Space to begin shape drawing again, and this time select Ellipse from the shape dropdown:
Once that is selected, move the cursor back up to the square on the right, and click 32 units away from top left corner of it, then click 32 units away from the bottom right to create a circle, as shown below:
Now we have two squares and a circle, hooray! Well ok it isn't much, but it's something at least.
Now that we have a basic room going, it's time to add a player start so that we can test this map in game. Without a player start, the map will bomb out if we try to run it.
To create a thing, we must first be in Things mode. You can do this by either pressing T (by default), or selecting 
things mode on the toolbar. Once in things mode, we can create a thing by pressing Insert or right clicking and selecting Create Thing Here.
Move the mouse cursor to the middle of the circle we drew last, and press Insert to create a thing.
And there we have it, a player 1 start.
Normally when creating a new thing, it will copy the type and properties of the thing that was previously edited. In this case, where we haven't created or edited a thing previously, it will create a player 1 start by default.
There is a small problem here though, the player start is facing towards the wall rather than towards the middle of the room. We don't want this, so let's change the direction it's facing.
The simplest way to change a thing's direction in SLADE is to use the quick angle edit feature. The default key binding for quick angle edit is D. If you move the mouse cursor over the player start and hold D, you will notice you can change the direction it is facing by moving the cursor to the point it should be 'looking' at. With this, change the player start so it is facing toward the middle of the room, as shown below:
Now that our map has enough in it to work, we can test it in-game. To do this, we can bring up the Run dialog. To bring this up, either press Ctrl+Shift+R, or select 
Run Map in the Map menu or on the toolbar.
Here we can set up a game executable to run, and any parameters we need to run the map. For this tutorial I'm going to select Chocolate Doom as the game executable, however you can select whatever port you want.
Once you have selected a port in the Game Executable dropdown, you will also need to browse for the actual executable on disk, by clicking the 
button to the right of the Path text box. Browse to the executable for the port you selected previously and select it.
We shouldn't need to set up anything else in this dialog to run the map, however you can find more information about the other features on the Run Dialog documentation page.
Finally, click Run to launch the game with our map loaded.
Well, it's definitely less impressive in game than it is in the editor - here it just looks like a rectangular room. We will need to edit the map further to make each part of the room different, so that we can actually see the two squares and circle we created. But that's for the next tutorial :)