A template remembers how a task is built, not what is in it: the stages and their delays, which exercises with which question-and-answer settings, which kinds of word card, and the extras. The words themselves are never stored in a template.
That is why the same template applied to another set gives another task. Everything inside is generated again from the words of the set you are working with, so a template is a plan you reuse, not a copy you duplicate.
Applying a template replaces the current plan in the builder completely, without asking. If you had already assembled something there, undo is the only way back — so apply the template first and edit afterwards, not the other way round.
A template is a snapshot in the other direction too: editing or deleting a template changes nothing in the tasks already built from it. Those tasks live on their own.
A name is between 2 and 30 characters. The template list inside the builder shows the twenty most recent ones; the Templates screen shows all of them. And deleting a template from that screen happens immediately, with no confirmation, so check the name before you press it.
One thing a template does not carry: the links you draw between elements inside a stage are not saved. After applying a template, set them up again.