Templates are basically example notes that fill out new notes you create. So if you want to pre-fill your jira ticket notes with a template like

ticket: ... ## Problem ... ## Solution

then you'd want a template. Schemas organize a structure in your notes. If you want all your jira ticket notes to be organized under

jira.2022.04.11.<area>.<ticket-number>

, you'd want a schema for that. Schemas can automatically apply templates to notes, so you also might want both.