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Buck-boost transformers are for converting 240 volt to 120 volt, or 120 to 240 Volt.
Household voltage is dangerous and should be worked on only when power if verified OFF.
Resource: Safe electric wiring
Buck-boost transformers are for converting commercial 480 volt to 240 volt etc.
Commercial 480-277 volt power will immediately penetrate insulating effects of skin and kill.
High voltage carries extreme hazard and should be worked on only by professional electrician.

Wiring example for step down
240 Volt input: 1 wire connects to H1 and H4, and then other wire connects to H1 and H2.
120 Volt output: 1 wire connects to X1 and X3, other wire to X4 and X2.

Insulating transformers share no wire between the primary and secondary side and achieve voltages using magnetic induction via the shared iron core. 

Autotransformers are a single continuous winding, where the primary and secondary voltages are electrically connected. The higher or lower voltage is achieved by having a tap along certain points in the coil of wire.
In the case of buck boost, one wire from high voltage would be connected to H4 and other wire connected to X1. Then X1 jumpered to X3, then X2 jumpered to X4, H1, H3, and H2 jumpered to H4. In other words, all 4 coils of wire inside the buck boost are connected into 1 long coil of wire. Then the lower voltage is connected to H4 and midpoint between X4 and H1.
Using the various combinations of autotransformer wiring, the transformer can be wired either way so high voltage is converted into low voltage, or low voltage into high voltage. Resource Buck boost pdf

-Best if transformer is located out of direct sun where heat can shorten life of any electrical installation.
-PX series transformers are manufactured specifically for electrical safety. They are designed to electrically separate or insulate the incoming 120 volt power from low voltage wires that go to pool. This ensures that low voltage wires going to the pool or to lights cannot be energized with high voltage.

Safety
-Never use 120 volt lights under water, or where wires or connections might come into contact with the pool or any pool liner ... even if wires are properly insulated. Why? Because insulation failure of coatings surrounding a wire are not uncommon with nearby lightning strike or short circuit. The result will put high voltage into the water that will cause electrocution if a person comes in contact.
-Never depend on GFCI for 100% protection. GFCI must be properly grounded, and must be tested before each use by pushing test and then reset buttons. Ungrounded GFCI will not trip immediately, and while an ungrounded GFCI will usually protect person, there is no guarantee. Two prong extension cords, and double insulated tools do not give complete protection even if plugged into GFCI. Always use 3-prong extensions cords and grounded power tools when working outdoors.
-Always use conduit for outdoor 120-240 volt wiring. Use approved 600 volt cables and wires for 120-240 volt household wiring. It is against code to use extension cord for permanent wiring. Resource: Color code for residential wiring