If you want to invite & allow your team member to use SalesHandy (Track emails & document, send email campaign & add templates), you as an admin user need to buy the extra user account. With this you can invite the team member in your account. Email address invited can signup on SalesHandy & use it.
If you want to add more email addresses as sending methods in your existing SalesHandy Account, you need to buy email account.
You can configure more email addresses using Google OAuth & SMTP within your SalesHandy account. Using this extra email account you will be able to send email campaign from another email address from your existing login.