Hi there Tony o/
Thanks so much for checking out the game. I'm sorry that it wasn't clearer. Let me try to assist:
There is a list of toys for the elf to make on the top right. The toy you are making at "present :P" is at the top center of the screen. beneath it is a list of parts required to make it.
On the left bottom there are parts that change. There is also a selector moving through them every 3 seconds.

Left clicking will move the currently selected part to the conveyor belt.
Right clicking will move the selector ahead of the 3 seconds.
When you have the parts on the belt, click the elf to complete the toy
if you were correct you get points and a toy
if you were wrong you get a corrupted nightmare version of the toy
I hope this helps!
Can Haz <3