After you create your group poll, you will see the option to "Share invite" on the participation page.
You'll then see the option to invite your participants via link sharing or via email invitation. If you chose to share via link, click "copy link" and distribute the link as you see fit. If you invite via email invitation, add the emails of the people you would like to invite. Below the email invitation field, you can edit the automated message that will go out with your invitation.