The syntax
is [thing to store] STO [variable]. Note that
x+1 STO f(x) and x+1 STO f are different.
The former
is a function; the latter is an expression.
Define [variable] = [thing to store] does exactly the same thing. (Define is the first option on the Other menu on the HOME screen.)
You'll get
an error message if you try to change the variable
type. (E.g., if f is already the name of a function, you can't store
a number
in it until you've "emptied" it.)
Whenever
the variable name appears later, the calculator will substitute whatever
you stored there for the variable.
This isn't
always what you want.
You can
"empty out" the variables x and xy by entering delvar x,xy on the
command line. Find delvar in the CATALOG or on
the Other
menu of the
HOME screen. NewProb
deletes all the variables with one-letter names.
So you want to use one-letter names for TEMPORARY storage, and multi-letter names for LONG-TERM storage.