You should either read Bill Bryson's book 'A Short History of Nearly Everything' or watch Carl Sagan's TV series 'The Cosmos' (on YouTube). I would recommend both as they will certainly answer your question.
What would aliens look like, you wonder. Well, wonder no more:
An unidentified "life form", from the planet NepOutofTune. Note how it takes on the very crude image of a human, in order to walk among us without raising suspicion. See too the total lack of any neck - scientists speculate that this is to protect their windpipes under a layer of fat from the harsh space environment. In fact, the whole shape of this organism is characterised by its distinct bloblike formation. Ever heard of the B-Movie classic 'The Blob'? This is essentially a newer version of that. Also, look at the billowing skirt like substance on her lower half. This is actually not a dress: this type of alien moves by floating along the ground - what you believe to be a dress is actually part of the organism's body itself. This creature has a very unusual method of attack. In a hideous inversion of the Sirens of Classical Greece, it sings in such an awful voice that all who hear it are instantly paralysed, whereupon the creature will devour its unfortunate victim. It wears a number on its chest: this is a clever evolutionary device to allow the creature to imitate a talentless weirdo appearing on a TV game show, where it will be able to sing (and thus feast upon) a whole audience. Simon Cowell is an especially delicious target for this evil race: his head is so large, and his bank balance so grossly inflated, that the creatures will be able to live off the carcass for years to come.
UFO stands for unidentified flying objects. That doesn't necessarily mean any flying object is an alien spacecraft. In the UK there have been a few official UFOs that the government never officially identified. We now know many of these were secrety US military aircraft being tested although I think the government probably knew this all along.
Aliens, well given the vast size of the universe it's probably likely that other lifeforms exist in our universe. Infact they probably exist in our galaxy. I highly doubt they have visited us though.
Last edited by Foghorn Leghorn; 02-07-2012 at 22:06.