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(emacs-lisp-intro.info)How to Evaluate

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How to Evaluate
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   Whenever you give an editing command to Emacs Lisp, such as the
command to move the cursor or to scroll the screen, you are evaluating
an expression, the first element of which is a function.  This is how
Emacs works.

   When you type keys, you cause the Lisp interpreter to evaluate an
expression and that is how you get your results.  Even typing plain text
involves evaluating an Emacs Lisp function, in this case, one that uses
`self-insert-command', which simply inserts the character you typed.
The functions you evaluate by typing keystrokes are called
"interactive" functions, or "commands"; how you make a function
interactive will be illustrated in the chapter on how to write function
definitions.  Note: Making a Function Interactive.

   In addition to typing keyboard commands, we have seen a second way to
evaluate an expression: by positioning the cursor after a list and
typing `C-x C-e'.  This is what we will do in the rest of this section.
There are other ways to evaluate an expression as well; these will be
described as we come to them.

   Besides being used for practicing evaluation, the functions shown in
the next few sections are important in their own right.  A study of
these functions makes clear the distinction between buffers and files,
how to switch to a buffer, and how to determine a location within it.