For the USB Switch inserts, they replace an existing 10a fuse within the cabin which is then added to the empty fuse slot on the wiring for the USB. Essentially this will continue to act as a fuse for the original socket whereas the 10a fuse included with the USB Switch is a stand-alone fuse for the USB itself. This can be very easily described using the graphics below.
Remove your selected 10a fuse from the fuse box and insert it into the empty slot on the fuse tap.
Place the fuse tap into the fuse socket that has been removed and lastly secure the earth to a raw metal surface within reach.