I cannot select certain parts of my board?
If you select by moving the mouse from upper left to lower right you need to completely enclose the object being selected in the selection box. If you move the mouse cursor from lower right to upper left, you only need to partially enclose the object in the selection box. 

Also, your part might be locked. That makes it harder to select. If that's what's going on, you need to locate the component in the PCB window and select it there, then unlock it.