If you want to invite friends, family, colleagues, readers or anyone else to sign up on the same Mastodon instance as you, try using the invitation system:
1. Click on "invite people" in the bottom left corner of the page. (If you're on multicolumn, click on the "invite people" link at the bottom of the Getting Started tab.)
2. Choose your invitation settings (uses and expiration date)
3. Click "Generate", then send a copy of the link to the people you want to invite
mastodon.at is a microblogging site that federates with most instances on the Fediverse.