There are three handbooks available, as pdf files, for users of the 20 m telescope.
The OSO 20 m Telescope Handbook contains a technical overview of the telescope, observing modes, etc. It also includes a description of the control system Pegasus, which in 2019 was replaced by a new control system, Bifrost (described in a separate handbook).
The BIFROST User's Handbook explains how to use the telescope control system Bifrost:
The document Onsala 20 m data properties - Important information for observers is intended for users working working with data from the 20 m telescope. It is a beta version and contains methods which are not tested in all details.
The telescope system is regularly updated, which is not always reflected in the documents above. The telescope scientist or astronomer on duty will provide observers with the latest information when needed.