One Point Perspective is when one vanishing point is used.
To draw a cube in 3D it quite easy and the steps are simple to follow. Make sure that you draw lightly so that your construction lines are easily erasable if and when you need to.
Step One: Draw a line border around your page/paper.
Step Two: Draw a horizontal line (blue line)across the top part of your paper.
Step Three: Add a point ( red dot) on the horizontal line 0n the right hand side of your paper. This point is the vanishing point.
Step Four: Draw a square in the lower left hand side of your paper.
Step Five: Draw lines (green lines)to the three corners of the square. These are construction lines.
Step Six: Draw parallel lines (orange lines) to make two sides of the cube. now you should be able to see a cube. If your lines are not parallel the shape will be distorted.
Step Seven: Now you can add color. It is important to use color in three values or shades. The square will have the darkest color because it is the closest to you. In perspective, the object or the part of the object that is the closet to you is the darkest color. Next the top will be the lightest because it is the most exposed part. and the remaining will be the middle shades.
Step Eight: To make the cube really look 3D you will have to add a shadow. In this case you can see that light is coming from the vanishing point so you will be adding the shadow from that point. Draw the shadow lines. (grey lines) Notice that one shadow line continues from one green line or one side of the cube and the other actually passes through the other corner/ angle of the cube.
Step Nine: fill in the shadow area with a medium shade of grey.
Step Ten: Erase or delete all construction lines except for the horizontal line. Attend to details and make sure all your lines are straight and colors are well placed.
Step Eleven: Put in your background color which would be light and your foreground color which would be dark. 
