1.
Add a district boundary file so you know where you are.
2.
Add a DEM raster: Layer – add raster layer and navigate to your DEM (if you dont have one you can down load a 90m DEM off the net.) This should look like a grey layer.
Note: DEM = Digital Elevation Model and has xyz values for every pixel.
3.
Click on Raster in the tool bar – analysis – DEM (Terrain models)
4.
Select the DEM in input raster, and select location and give name for the output file which will be the new slope raster file that you will create.
5.
Set the Mode to Slope and decide whether you want it in % or degrees.
Now set the scale to 111120. This is because the vertical height is measured in metres but the horizontal distance is measured in degrees (WGS84)
6.
Click load into canvas when finished and OK, wait a minute it may take time to calculate.

7.
It should come up as a single grey colour.
8.
Double clip on the layer in the left hand bar and in the style tab choose colour map, then in colour map tab put in 5 entries down the bottom and classify.
9.
You can reassign the values and the colours and the labels of your classification.
10.
Click Apply and OK and check it out.

Notes on Slope Calculation from the website: http://www.gdal.org/gdaldem.html
slope
This command will take a DEM raster and output a 32-bit float raster with slope values. You have the option of specifying the type of slope value you want: degrees or percent slope. In cases where the horizontal units differ from the vertical units, you can also supply a scaling factor.
The value -9999 is used as the output nodata value.
The following specific options are available :
-p : if specified, the slope will be expressed as percent slope. Otherwise, it is expressed as
-s scale: degrees ratio of vertical units to horizontal. If the horizontal unit of the source DEM is degrees
(e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical units are meters (or scale=370400 if they are in feet)