How do I create a group contact list on my iPad?

You create a Contact List (i.e., a Group), within your Contacts App, for the intended recipients.

Each member of the list must have a contact card within your Contacts App - obviously with the recipient email address.

To create your list, ensure the Contacts Sidebar is visible; tap the Sidebar button at top-left of the Contacts Window to expose the sidebar.

To create a new list, tap the Edit button at the top of the sidebar - then tap the Add List button at bottom-left. Give the list an appropriate name, then tap Done. Next tap the new list that you have created; this will open the list editor, where you can add contacts to your list with the Add Contacts button - adding additional contacts as required.

When you’ve finished, you can use the Contacts List(s) that you have created (by name) for Messaging or Mail.

You're very welcome. Many tasks are straightforward - but until explained/learned, may not be immediately obvious. 🙂