There are several kinds of text editors available here.
E is the display editor in current favor.

SOS is teletype oriented.  If you will be using the display
facilities at the lab, learn E.

We also have a dialect of TECO.

To learn E, use the monitor command: HELP ETEACH

SOS is described in SOS.LES[S,DOC], and briefly by HELP SOS.
TECO is described in TECO.MRC[UP,DOC].