There are three basic letters you need to remember for this:
A A A A A A A A
B B B B B B B B
E E E E E E E E E
The A KEY selects everything or deselects everything. When a vertex or vertices are selected they will turn yellow.
The B KEY will select. Press it once and it will be a box select. Press it twice and it becomes a circle select.
The E KEY extrudes. Extrude means to pull out and create new objects.
*****When you are asked to press NUM keys or letter keys make
sure you are in the gray work area with the boxes. This picture shows you
the gray work area.
*****
Start Blender.
Press NUM 1 to enter front view.
Press Tab to enter edit mode.
Press the A KEY to deselect all vertices.
Press the B KEY. This key is used for selecting. It will select the vertices that you cannot see that are there.
Drag a box across the top 2 vertices.
Press the E KEY. Click Region.
Hold the Ctrl KEY and drag your mouse up 7 units.
Press the A KEY to deselect all vertices.
Press the B KEY to select the two side vertices at the
bottom. 
Press the E KEY and then click region.
Hold the Ctrl KEY and drag to the right 4 units.
Press the A KEY to deselect.
Press the B KEY to select.
Select the 2 vertices which will soon become our next
building. 
Press the E KEY to extrude. Click Region.
Hold the Ctrl KEY and drag up 5 units.
Continue this process until you 6 or 7 buildings.
Now we will build the street. Press the A KEY so all vertices are deselected.
Up till now when you use the B KEY you select vertices that
you can't see. We are going to change that. We are going to
limit selection to only the visible vertices. Click this button
It is the cubed picture.
Using the B KEY select all the vertices at the bottom.
This will become our road.
Press NUM 7 to go into top view.
Press the E KEY and Only Edges.
Hold the Ctrl Key and extrude 5 units.
If you rotate your view a little you will see you have one
side of your city.
Press NUM 7 to make sure you are in top view.
Press the E KEY for extrude. Click Only Edges.
Hold the Ctrl KEY and extrude 2 units.
This will
become the other side of the city.
We are now to switch to face select. Click on the
triangle with the dot on it. 
Right click on the first face on the left.
Press NUM 1 to go into front view.
Press the E KEY for extrude.
Hold the Ctrl KEY and move up a few units. You decide what would look best.
Press NUM 7 and select the next face.
Press NUM 1 for front view.
Press the E KEY for extrude.
Extrude this building up.
Continue this process until your city is done.
Click on the this box and enter object mode.
Press the Shift KEY and the F KEY to enter flight mode.
Fly around your buildings.
If you have extra time keep on building your city.
In the bonus area you are going to continue your city with street corners.
Click Edge select. 
Press NUM 7 for top view.
Select the edge your street ends.
Press E for Extrude.
Hold CTRL and extrude out 3 units.
Select the new side street and extrude that up 2 units.
Keep extruding up to create your new street. Each time
you extrude it shouldn't be more than 3 or 4 units.
Now we need to create space for the new buildings.
Press the A KEY to deselect.
Press the B KEY. Draw a box around the sides.
Press the E KEY.
Hold the Ctrl Key and move 2 units to the right.
Now do the same thing for the other side of the street.
Go into face select mode and extrude your building up.
To extrude quicker click several faces at a time. Here
is an example: 
Did you
notice that I picked random pieces. To select more than one mouse hold
down the Shift KEY when you select more than 1 face.
Go on and finish all 4 sides. Here is my example.
Once you have a city like this you can build the rest easily by duplicating.
Press the Tab KEY to go to Object Mode.
Press NUM 7.
Make sure your city is selected. If it is not selected right click it.
Press Shift D. This will duplicate the city.
Hold the Ctrl KEY and move your mouse to the side.
Now my city is bigger with a little bit of work.
You can duplicate the rest of the city pretty easily.
