Send a message to 23559 and it will get sent to your "current cell" (the last cell that you joined or messaged). This is simple if you only have one cell. If you have multiple cells, start your message with the @cellname prefix. For example, you might text: @classroom123 don't forget the pop quiz tomorrow! -- and your message will go directly to the cell @classroom123.
If you have multiple cells and you forget to add the @cellname prefix, you will receive a confirmation message allowing you to select a cell. All of your following texts will go to that cell until a member from another cell messages you. If this happens, Celly will again ask you to specify which cell you want to message.
For more info, with screen shots, please view our guide: How to Chat on a Cell