There are 2 types of communication templates you can create:

Event attendee and Lead

The difference being the tokens available to use. For example, creating an Event type communication template will enable you to use the event form tokens, such as 'Attendee First name'.

When creating a new email, if your template isn't appearing in the list, check the template type. If your template is setup with the wrong type, you can edit the template. Just make sure to check any tokens you have used are still valid.