Learning Scheme - atom, list and S-expression

It looks it would be easier to go through The Little Schemer first before pick up SICP, so here we go.

atom is the most basic building block, it could be a letter, a string of digits, a string of characters. Examples:

a
1492
atom
*abc$

list is one or more atom enclosed by parentheses. Examples:

(atom)
(atom turkey or)
((atom turkey) or)

All atoms and all lists are S-expressions. For example, there are three S-expressions in the following example :

(((how) are) ((you) (doing so)) far)

They are ((how) are),((you) (doing so)) and far.

The null S-expression:

()