I've been trying to teach myself how to use Sketchpad & going to the Tuesday webinars, but I'm stuck and need a bit of help.

I've used the getting started tutorial and thought I understood how to create a new function. When I use Plot Function and enter the equation from the class textbook, it appears correctly. The problem I run into is when I try to make "x" into a parameter.

I define a parameter. When I edit the function, substituting the newly made parameter into the function, it stops recognizing the function. So if I had f(x)=2*x, and now my parameter is x=3, it plots only the x=6.

I tried to attach my sketch(which is very basic) to see if you can help me find my mistake or help me understand where my thinking going awry. 

Thank You!!!

I didn't find the right solution from the Internet.

References

http://sketchexchange.keypress.com/forum/showthread.php?114-Working-with-functions-and-parameters

Flat Animation Video