1-Ups are special items in Star Fox, Star Fox 64, and Star Fox: Assault.
In Star Fox, 1-up assemblies can be found in various levels. They appear as three blue and red objects arranged in a triangular and vertical ring; shooting one of them will cause them to rotate, and shooting all three will cause the 1-up to appear in the middle allowing you to fly through and obtain it. The easiest way to go about all this is to shoot one of the ring parts and then simply let the others rotate into your line of fire, while using your brakes to slow your speed.
In Star Fox 64, they can be earned by points or collecting three golden shield rings a second time on one stage. They can also be found on some of the stages, but they are very rare. They are in a shape of an Arwing
In Assault they are usually hidden in either places, that are hard to reach or that nobody would expect.