An Email Templateis exactly that, a template you use for sending emails. When you create a new Mago:Talent account you are provided with several stock email templates covering everything from sales letters and follow-ups to templates for several common situations (e.g. declining a gig or reminding a contact about a late payment)
Every template in Mago:Talent supports merge fields. A Merge Field is a placeholder that, when you use a template, will be replaced with a value from Mago:Talent.
For example, instead of just copy-pasting an email you sent to another contact and changing all the fields by hand (and risking missing a wrong name or a date and confusing your contact) Mago can perform a merge automatically customizing the email for that contact and gig.
When creating or editing a template, all merge fields are accessible under the "Insert" menu.