Discusses the source of the 39 Melachos, which are learned based on the Melachos that were done in the Mishkan. We will discuss why this source makes the fundamentals of ma'aseh melacha a unique category, different from all other forbidden actions. With regards to ma'aseh melacha on Shabbos, one's intentions alter his chiyuv. In addition, if an action is performed kilachar yad, it would not be considered Chilul Shabbos min haTorah. Many practical examples (i.e. Boneh, Kosev etc.) have been included.