When you say that you've downloaded maps of Liberia, I have a feeling that you're downloading raster images of a map or otherwise "complete" map and not individual data layers that you can work with.
You may need to look for shapefiles or a geodatabase with Liberia county or other administrative district polygons. If you can find some that already have attribute (census or other statistical data) attached, you're ahead of the game. I was able to find some possible data by searching Google for "liberia county shapefile" without the double quotes.
Then you can choose to change how the polygons are symbolized.
Add the shapefile or feature class to ArcMap. Right-click the layer in ArcMap and open its properties.
Switch to the Symbology tab. In the left box choose to show by categories or quantities.
If your statistical data is table-based, it will need to have a common field (like county name) so you can join it with the county polygon shapefile/feature class.
Hopefully, this will help you get started.
Melita
