This is my very first time of using masks and I am testing masks. I want to know how to mask areas of a video. FYI, I am new to mask nodes. For any assistance, thanks in advance.
You can press Alt+C to Toggle Cyclic, which closes the selected splines. Pressing it again will re-open the mask spline.
This is also found in the Toolshelf (T) in the Mask tab> Mask Tools> Spline section or in the UV/Image Editor header under Mask> Toggle Cyclic.