There are six kinds of Supertech Inventions that you can build yourself (Superchemicals, Super Gear, Super Armaments, Doohickies, Ray Guns, and Gizmos). Doohicky, Ray Gun, Gizmo, and Superchemicals); these are always supertech. There are two other items that are most commonly supertech, Gadgets and Power Armour, which you buy with CPs.
Metapowers can affect Supertech Inventions, but in limited ways, as indicated by the metapower descriptions. Power Leech doesn’t work on Superchemicals, for example because they don’t have PPs, but it could work on a Ray Gun. On the other hand, Power Nullification or Duplication could work on all three because it acts directly on powers.
Super Armaments and Super Gear are use-activated. If you can use the mundane version of a super weapon, for example, then you can use the super version. Superchemicals have to be ingested or injected.
Doohickies, Ray Guns, and Gizmos all require special activation. The steps are (a) Fiddle With The Knobs, and then (b) Make It Go. In order to do either of these things, you must have the power Supertech Invention or the skill Use Device.
Fiddle With The Knobs: Make a Powercraft skill check, the DC of which equals 5 + the base cost of the most expensive power loaded into the Invention. If you pass the check, then you know one of the Invention’s powers. If you fail the check, you have discovered nothing.
Make It Go (aka “Make It Go Boom!”): You must have the Invention in your hand. Activating a Invention provokes an attack of opportunity. The effect the Invention creates is exactly the same as if you’d activated the power that’s loaded into it. All the specifics of its effects (enhancements/limitations, energy type, etc.) are determined when the Invention is built. You just push the buttons, and it does its thing.