What exactly is it to be asexual ?

I heard that these people think sex is gross or are beyond celibate. They can have relationships but just dont get sexual. Every human being has some type of libido, how is this possible? the internet gives all sorts of confusing facts, but I curiously want to hear from people. Also wen you're "asexual" is it hard to be able to love or find someone attractive physically and emotionally?....as if you'd reject half the world?