On the web:
- Go into the cell and click the "members" button. Next, click "invite new members". Enter in the email addresses and Celly usernames of the people you want to invite then click "invite".
- Send the web link to your cell through email, or by sharing it via Facebook, Twitter, Reddit, an online forum, etc. This generated link is located in your cell in the right hand column under "share". If you're the admin or curator of a cell, you can also send a golden ticket link that lets anyone join your private cell instantly. For more info, see this guide: How to Invite Others to a Cell
- Tell others to join your cell by texting @cellname to 23559. For example, if your cell is called History103 you would tell others to join by texting @history103 to 23559.