When you set up your group poll, you will see the option to add participants just underneath the meeting information section. Here, you can add the emails of your participants.
If you want to add more participants after you have already created the group poll, you can click on "add participants via email" at the bottom of the participant list, or click on "edit meeting" and add new participants in the "add invitees" field.
You can also skip the email invitation part altogether. You can choose to simply share the participation link as you see fit. Click on "share link" at the top right corner to copy the participation link.