Don't worry, functions in C2 are as operational as they are in pure JS.
You can use the function parameter by calling the expression "Function.param(X)", X being the index of the parameter.
I use functions in lots of cases. For example :
<img src="https://www.scirra.com/images/articles/TLE7_2.jpg" border="0">
(this is explained in a tutorial linked in my signature).
Also, here is a capx I made some times ago to explain the basis of functions.
Finaly, you can take a look at the function reference in the manual. The end of the article will explain all conditions/actions/expressions of the function plugin.