Check out this video demonstrating how to use the block feature within SolidWorks to create sketches that behave like linkages, cams, or gears. Blocks take a group of entities and lock them together. These are able to be moved, rotated, copied, and scaled very easily. Using blocks to simulate linkages is a very quick and easy way to check to see if a linkage system will work without having to design an entire assembly. I hope this tutorial will help you when designing mechanisms such as linkages or gears.
Ian Jutras