Insert Edges in Surface / Divide Surface
3-D Standard > Tools > Edge 
> Insert in surface 
You use this function to insert edges into the active part. This function enables you, for example, to divide the side of a dice into two surfaces, which can be addressed separately.
Specify the start point and the next points of the new edge. Choose END to end the function.
Left: Original - Centre: Part with new edges - Right: Divided surfaces
