Print the value and documentation of a variable.
Change the value of a variable.
To examine the value of a single variable, use C-h v
describe-variable), which reads a variable name using the
minibuffer, with completion. It prints both the value and the
documentation of the variable.
C-h v fill-column RET
prints something like:
fill-column's value is 75 Documentation: *Column beyond which automatic line-wrapping should happen. Automatically becomes local when set in any fashion.
The star at the beginning of the documentation indicates that this variable is an option. C-h v is not restricted to options; it allows any variable name.
If you know which option you want to set, you can use M-x set-variable to set it. This prompts for the variable name in the minibuffer (with completion), and then prompts for a Lisp expression for the new value using the minibuffer a second time. For example,
M-x set-variable RET fill-column RET 75 RET
fill-column to 75, as if you had executed the Lisp expression
(setq fill-column 75).
Setting variables in this way, like all means of customizing Emacs except where explicitly stated, affects only the current Emacs session.