I typed fr<TAB> as is written in the manual but got only a fr and a tab. The \frac{}{} is not correctly inserted and so does sq. Why is this happening?
By typing C-c ? you can activate the CDLaTeX Help, in which you will see TEXT/MATH, TEXT/, or MATH. This means that the function or abbreviation can only activated in the text mode, math mode or both of them of latex.
Insert the desired command between $$ to activate it.
This is pretty much a LaTeX problem than an Emacs problem.
emacs -Q(no init file). – Drew Aug 3 '17 at 4:30