Each of the Gedmatch admixture tools has an explanation by the scientist who develped it. In addition, you may find these sites helpful:

https://sites.google.com/site/wheatonsurname/beginners-guide...

http://www.isogg.org/wiki/Genetics_Glossary

In addition to Gedmatch, for genealogy you can transfer your Ancestry raw data to Family Tree DNA, which has more UK and continental participants. There is a fee of $39 to see all of your matches, although you can see the top 20 at no charge. The information is here:

https://www.familytreedna.com/AutosomalTransfer

For health information, see https://promethease.com/ondemandlicense

Jim