Content in “design”

I have a fairly strong background in code development, but I would like to build a stronger knowledge in curcuit design. I can read a datasheet and learn how to hook up a certain component, but when it comes to using a specific component for a use other than it is designed for I lack the knowledge to know when to use a capacitor, flyback diodes, etc.

I'm not positive this is the right place to post this.  Admins please move it if I'm asking in the wrong place.

As said in sociatyofrobots.com, designing is the most important stage of robot building. I spent no time designing Turpis, and that's most likely why it turned out so bad. However, I'm an awful artist, and I need to find a more efficient way to plan. I've tried my hand at Sketchup, and it is uncooperative with my computers. Are there any easy-to-use free software out there?

Thanks,

Brennon