Hi Liz,
Evidence Types are just files which can be used in conjuction with competencies - so types are user-defined. They arent tracked by the system - they could be scans of conference tickets, pics of work done, receipts for travel, certificates etc.
Theres some documentation here
http://help.totaralms.com/The_Evidence_Tab.htm
hope this is useful,
cheers,
George.