Whats the difference between a UFO and a UAP ?

Answer 1

One of them has "F" as a second letter and "O" as a third letter while the other has "A" as a second letter and "P" as a third letter.

Seriously, UFO stands for "Unidentified Flying Object" while UAP stands for "Unidentified Aerial Phenomena".

Usually UFO and UAP sightings (and they are typically the same thing) are things like the planet Venus (though Jupiter often gets mistaken for an alien spaceship), aircraft, birds, satellites (especially ones burning up) and other things of that nature not all of which can really be called flying.

The sightings that aren't things like that are probably either delusions or lies (not alien spaceships, no one has ever actually found any evidence that aliens exist).