We are in the process of rewriting help pages for paypal button but for now see http://help.wildapricot.com/display/DOC/Inserting+HTML+forms and for other specific paypal button codes you would need to use go here https://www.paypal.com/IntegrationCenter/ic_standard_home.html.
I am not sure I quite understand what you are trying to do with a donation template - do you want to change the donation form? If not I would simply use a link to the donation form and make the donation form a child of an invisible form, see http://help.wildapricot.com/display/DOC/Subpages+and+multi-level+pages (see hint at bottom of this help page)
If on the other hand you are looking for a custom form, look at Wufoo forms instead, see http://help.wildapricot.com/display/DOC/Adding+custom+online+forms+via+Wufoo
Jim Sympathy, Fluid Apricot