TL;DR: Invite agents by email from the team admin Dashboard. They accept, sign in at app.asksayso.com, download Sayso, and start calling on your team's hours. Invites expire after 7 days.
Ask agents to use a personal email they'll keep. Login emails can't be changed later.
New members draw from your team's pool. Set how many hours each agent gets. See Allocating hours to team members.