To add or invite someone to your Squad you must be an admin or creator of the Squad. Then, click on the add people icon at the top right of the webpage near the chat icon.
There's two ways to invite others, to invite by email, enter the person you'd like to add email, and a default display name will be created, you or the invited user can change their display name later.
To invite by link:
Click on 'Link' on the Invite people pop-up, then a custom link to the app and your Squad will be created, anyone with this link can join SquadPod, and joins your Squad. Share it via social media, text, or even email. From here you can also revoke a link, or reset a link for a new link url.
Check out Managing Roles and Permissions to read more about each role in squads, pods, and group chats.