This video demonstrates how to download and install the SolidWorks Software Development Kit. It is part one in the series because the SDK is the easiest method for creating a new add-in.
Creating a SolidWorks Add-in using the SDK is very simple, but a lot of people have trouble getting it set up in the first place. If you have an active subscription it is possible to download it from the customer portal. Just follow the steps in the video below. Please note that the SDK only works for full versions of visual studio.