I am assuming that you want to find the volume of a cube of side length 7? As well as its surface area.
The best way to think about this is by first using the formula for a rectangular prisms volume as a cube is just a special form of rectangular prism. The volume formula in question is length * width * height = Volume. Just plug in the measurements. (Remember: A cube is just a rectangular prism where all sides are the same length in your case 7).
Calculating the surface area of a cube is much easier than that of a rectangular prism. The best way to do this (for a cube) is to find the area of one of the 6 faces of the cube. It is length * width =Area. However, you know that a cube has 6 identical faces so you can multiply the Area *6=total surface area of a cube.
To Calculate the surface area of the rectangular prism the best way is to draw it out. Calculate the Area of each of the faces and add them together. Or if you realize that opposites sides are the same area you can just calculate 3 different surface areas and multiply them each by 2.
I hope this helps... I do not want to give you the answers as you need to practice to learn. If you don't understand something I said just post back and I will try to help you better understand.