It’s very straight forward, at the input side you have to connect two power sources and connect the output to the receiver, if you’re using an ESC with a BEC, UBEC, SBEC or similar, connect it to the input marked with triangles since that’s the one connected to the signal pin at the output, then the output has to be connected to the throttle channel in the receiver.
The voltage input can be up to 50V but each diode can stand up to 3A, normal use will be 5V and 1A. When the two inputs are connected the current will be divided between the two diodes, if one stops working the other will keep supplying current and the total consumption of current will flow through one diode.
Try to use a higher voltage in the main power or lower in the auxiliary power supply so the auxiliary battery doesn’t drain as fast, it could be 5V from the ESC and 4.5V from the auxiliary. This is not critical but be aware that you’ll have to charge the auxiliary battery as per normal, and check its voltage after every flight.
You can use this system in an airplane with up to 4 standard servos or 6 micro servos, that’s what I recommend since each diode only allows 3A but depending on how much current your servos draw and the use you give them, servos draw different amounts depending on the torque they have to work.