There are a number of options in the floating toolbars that dictate what entities are allowed to be selected from the screen, and how you can select them.
Of the selection tools, Filters are the most important. Filters control what type of entities (objects, faces, curves, points, etc.) you are allowed to highlight and select at any given time. All Cimatron functions have default filter settings, based on what would make the most sense for the function. But you can add or remove to the filter status to help you select the exact geometry required.
Another selection option is single pick or box pick. There are new varieties of box picking that you can choose from: User defined polygons, Lasso mode, or Brush mode. Brush mode also allows single selection, and has an adjustable brush diameter.
If you do need to select an entity on the back side of the part, you can use the "pick through" selection tool. There is no icon to enter this mode, just let the cursor sit a moment on the screen. The cursor icon will change from an entity to an arrow. The arrow is the sign that the mouse is ready to "pick through". Now roll the mouse wheel away or towards you to highlight all the possible geometry for selection. Release the mouse and select when the entity you want is highlighted.