Yes but they can and do go to the bottom of a tank too.
Yes, Guppies are obviously surface fish. Just look at the shape and angle of their mouths. You can see that they are designed specially for skimming under the surface of the water.
It faces upwards for feeding from the surface and is in front of the fishes eyes.
Guppies, like all fish, have gills and breath oxygen that is in the water. I have observed though guppies going to the top of a tank for surface air and surviving by doing this.
Guppies are surface fish and they also enjoy swimming/playing in water currents that is why they are there.
I hope your tank is large enough for the 7 or 8 inches of fish you have in there. (1 inch of fish needs 1 gallon of water). Shortage of oxygen will cause fish to go to the top/surface for air. However Guppies (Poecilia reticulata) are naturally surface feeding fish so that is where I would expect them to spend most of there time. Surface feeders are easy to recognise simply by looking at the construction and shape of the fishes mouth. Note that it tends to open in such a way as to skim the surface of the water.
Fries (the term for baby guppies), are eaten by older guppies, but guppies are eaten by fish like tuna.
That would be a snorkel.
What are guppies
Only guppies breed with guppies naturally.
No, guppies are fish.
Guppies do not migrate.
Guppies are compatible with Bristlenose catfish, the bristlenose being one of a few catfish that can live with guppies because of the guppies' water.