To get you started with creating your own maps, I'll give you a short explanation of the editor functionality.
Basically, building a map consists of these steps:
Building your network
If you want to base the network on an actual area, you can load a map image into the editor. This allows you to easily draw tracks over the image in the background. This is the first thing you should do because you cannot move the image around to fit any tracks you may have built earlier. However after you've imported the image make sure you set the editor to the right scale using the Image-Set Scale menu item. For example: the raster width is currently set to 100 m. If the width of the raster corresponds with 500 m in the map image, fill in 500 in the 'Desired Raster Width' box. That will zoom the map image as much as is needed to have the raster width correspond with the map scale.
Now draw your first track. Switch to track draw mode (the button marked Tr or just press F6). Use the left mouse button to draw a track line. You can see that two GNode's have been created, with a line of track between them.
If you switch back to select mode (F5) you can move the GNode's. You can connect the next track to a node in track draw mode (F6) by left clicking on a node and holding down the mouse button while drawing another track.
Note: you can move the map by right-clicking and moving the mouse.
Double track
Let's change the last track into double track. Add a node to both the GNode's by right-clicking on the GNode and select Add Node. It's important where you click because that determines where the new node is added or inserted.
Now you can easily draw a new track between the two new nodes.
You can build additional double track from this starting point by holding down the Control button and drawing track from a multi-node GNode.
Switches
Building switches is very easy: just draw a second track on the same side of a node. Each node can have two outbound tracks on both sides. Usually a switch will be one-sided (ie one inbound track and two outbound) but both sides can function as switches.
Building stations
A station is built by adding a platform to a GTrack (a group of one or more tracks). Add new nodes, then go to platform draw mode (F7) and draw a platform between two nodes. There has to be an existing GTrack connection where you add the platform.
The purple dashed line represents a platform. This GTrack is now a station. If other GTracks with platforms are connected to this one, they will form a single station together. Right click on the station and select Station Properties to set its name and type.
Defining lines
A line defines the route taken by trains running on that line, as well as the stopping stations for the trains on that line. From the List menu, choose Lines to see a list of lines that have been defined. Add a new line called 1 and choose its type.
Stations
Whether a train stops at a station is determined by comparing the station type with the line type. Trains stop at all terminal stations, but only stop at local stations if they are running on a local line.
Switches
The most important part of defining a line is setting its route. This is done by setting switch directions for all the switches on the line. Right click on a switch node and select Switch Properties.
As you can see in the example above, the switch has a default direction set to Left. This is of course the left in the direction of travel. You can change the default direction and you can add or remove lines to the 'Lines routed off default direction' box.
Now that the line has been defined, it's time to add trains.
Adding trains
Place a train on a track by dragging the train icon on the left to a node (the icon itself doesn't actually let itself be dragged but it'll work anyhow). The new train will be placed at this node in one of the available track directions. The New Train dialog box lets you edit the train's properties. Set the line number to the right value, and figure out how long you want the train to be.
You can recognize the train direction by it's 'lights'. The front of the train is marked by a white dot, the rear of the train (though usually drawn behind the GNode) is marked by a red dot. You can reverse the train by right-clicking on it and selecting Reverse Train.
Defining a timetable
Without timetables, you have little control over the movements of the trains (except with the autopilot switched off). Even when you distribute the trains evenly along a line, there's no guarantee it will stay that way. It is therefore advisable to create at least one timetable along each line. A timetable is a list of departure times which applies to a certain line, at a certain station in a certain direction. First let's look at the line schedule.
Schedule
Choose Lines from the List menu, then go to the Properties of one of the lines. You should see something like this:
Once there is a train with this line number, Tred attempts to build a schedule. A schedule is a list of all the stations along the line that the train is running on. As you can see here, trains on line number 1 run from station North to Bank, then to Main. The last station is Panini, where the train reverses and runs back to North (this is not being represented very clearly at the moment). The schedule shows at which stations the trains will stop. This is based on the type of line against the type of station as explained earlier. You can change the line type here and see what effect that has on the stops.
The arrival and departure times shown here are estimates relative to the departure from the first departure point. You can use these to help you build a timetable, but they have no other use in the editor or the simulator.
As you can see some of the stations have an 'x' in the timetable column. These are stations that have specific departure times that all trains running on this line will wait for. Select a station in the schedule and click Timetable to view, edit or create a timetable for this station. (Note: make sure you pick the right occurrence of this station in the list, because there can be different timetables for the different departure directions. For example, station Main has two timetables, one for departures in the direction of Panini, and one for North.)
Timetables
The timetable window lets you enter all the departure times for the selected line at the selected station in the selected direction. In the simulator, a departure signal post will be placed at the end of the platform. The signal will turn white when the train is allowed to leave (according to the timetable). Note that this signal has nothing to do with safety; there is no guarantee that the track beyond the signal will actually be free. However since the simulator does not (yet?) have the possibility to show you the timetable, you can use those signals to let you know it is time to depart.
Finally, don't forget that the departure signal has a different function than the departure light in the cab. When the departure light in the cab turns green, the train is ready to depart as far as passengers are concerned. This has (perhaps strangely) nothing to do with the timetable.