Picture of Draw Kerf Combs in Autodesk Inventor
This Instructable is designed to be a friendly project-oriented walkthrough for users new to Inventor or CAD in general.  If you want to start using Inventor like all the cool kids, but feel overwhelmed by the panoply of features, options, and tools, start here! 

We'll learn about: 
Sketches and parts
Setting the Heads-Up Display and using it to define dimensions
Drawing lines
Using the Mirror tool

Plus, you'll have a design for a pair of handy test pieces to help you figure out how to size your laser-cut boxes so they snap together just the way you want!  (To make the combs, continue through Exporting Inventor Files to CorelDraw [forthcoming], then cut them on your handy local laser.) 

Step 1: Make a new part

Picture of Make a new part
First, fire up Autodesk Inventor and create a new standard part.  A "part" consists of one or more sketches.  These sketches define one aspect of a part, such as the shape of one face of a part or the contour of a machined edge.

Select Standard.ipt and click OK to start a new sketch.