The menu Arrange is only active and available when more than one frame is selected on the working sheet. It offers you the commands to align the frames on the sheet (see next chapter).
To back and To front arrange overlapping frames by putting the selected frame to the very background or the very front, to a different layer.
If you want to have your frames in the same exact size, you select those frames and use the commands Same width and Same height. The first selected frame is the reference frame that the other frames will refer to.
Same space horizontal and vertical allows you to bring the distance between several frames to the same size in one step. Again, the first selected frame is the reference frame for the other frames.
The alignment of frames is described in detail in the chapter Alignment.