The Multiply Texture is used to multiply the values of texture or colors together like in the photoshop or any other painting or compositing softwares. There are only two options in this node: Tetxure 1 and Texture 2. Both must be used for to see the effect.
HOW TO USE
Open the Node editor and prepare the setup as you see in the picture below. In this setup two different textures (marble and checks) used for the "Multiply Texture" node. The in between gradient nodes are used for different purposes as you see in the picture below. İt's very simple setup for a simple node.