Mapping with GIMP
Here is a pretty basic video of how I go about making a map using GIMP. I have some of the links down below that you will need. I kinda go through this a bit quick, but I would be happy to answer any questions or clarifying something. I may do a much slower step by step video for this series in the future.
Regarding the brushes and the Script Fu plugins, you will need to Google how to install those. I did it a long time ago. It was pretty quick and straightforward though. And I am sure you can find videos on how to do it as well.
Links:
GIMP: https://www.gimp.org/
Map Brushes: http://starraven.deviantart.com/art/S...
Parchment Texture: http://www.deviantart.com/art/Old-pap...
Script Fu: http://registry.gimp.org/node/186