There are times when simple sketches are adequate for your design process, but you will often need to work on more complex sketches requiring a rich set of geometric or dimensional constraints.
What are Constraints? Creating Contact Constraints What about Constraint Visualization? Quickly Creating Dimensional/Geometrical Constraints Defining Measure Directions Modifying Constraints Creating Constraints via a Dialog Box Modifying Constraints On/Between Elements Fixing Elements Together Auto-Constraining a Group of Elements Animating Constraints Editing Multi-Constraint