If you are not familiar with WebFCML, FCML is an easy to learn computer language used to describe a level (or design). Say you wanted a yellow square (a dynamic rectangle) that is located at the coordinates of 15 x 20 and is 400 units wide and 100 units high, and you wanted to write this in FCML. Well, it would look like this:
DynamicRect (15, 20), (400, 100), 0
The 0 at the end means that the object will be rotated 0 degrees.
To get started with WebFCML (an online editor that allows you to save levels in FCML), check out a tutorial that some Contraptionistas put together.