If you are using the keyboard or mouse, simply right click the folder you would like to pin to the start menu, and select "Pin to Start" in the drop down menu. If you are using touch, hold down on the folder you would like to pin until a little box appears under your finger. When the box appears, release your finger and a drop down menu will appear. Tap "Pin to Start" in this drop down menu, and you will be successful in pinning your folder to the Start menu.