I read that the option formchar specifies the formatting characters used to construct the lines in some procedures. There are 20 characters listed in the system option as default. How do we get to know which character specifies for what?
SAS system documentation and search on keyword FORMCHAR. You will find references to the system and also there are specific PROC references where you will find the position information revealed under the formatting-character explanation. Another option is using the SEARCH facility at the SAS support http://support.sas.com/ website where much of the discussion (and more) is also provided.