Picture this, I have two components and that have been created about the same time. They have holes that line up, they have matching iProperties, their Parameters are very close to each other, and they even have similar materials. Sounds like a perfect mate. Only with this we are not talking about two components getting married and settling down and creating patterns of themselves. Here we are talking about constraining two parts inside Inventor's Assembly environment.
Inventor's Assembly environment controls how parts interact with each other and the parametric relationships they share. One of the ways to put parts together in this environment is by using assembly constraints. If you are a veteran to the software, this might be common knowledge to you and you should skip to the next paragraph. For new users, especially those coming from an AutoCAD background, this may seem a little foreign. AutoCAD users normally place parts drawings together with other part drawings into a single assembly drawing by use of blocks, x-refs, or heaven forbid copying and pasting. Contrast that with Inventor which uses an assembly file (.IAM) to maintain external references to parts placed inside it rather than actually copying the parts into the file. This is a basically super x-refs to AutoCAD users because they require very little care and upkeep. This associative relationship is a very strong point to use parametric modelers in designs that require faster productivity of updating large amounts of files and just about anything else your Project Manager or Sales Engineer can throw at you.

For your enjoyment and educational prowess I have created a simple Inventor Mate Constraint Game which focuses on one of the main types of Assembly Constraints that can benefit new and veteran users. For new users they will learn some of the basics and for the veterans I have included a few extra tips that you might have missed during your professional or self-training. The game is actually quite entertaining while you are waiting for a meeting, on lunch, or have some extra down time to burn up.
//IQ Block