In ProE surface modeling, most of the time you will build a surface model by creating pieces of surfaces adjacent to the other. In order to convert the surface model to a solid part you have to first merge all the surfaces. For this purpose you have to use the “Merge” option.
Click the “surface-1” and “surface-2” by pressing Ctrl button and then go to Edit → Merge. The Merge dashboard dialogue box will appear where you can change the directions for each of the surfaces. For our model (Figure-1) after merging it will appear like below:

click to enlarge