A)I think that a 'web celeb' is the one who shows his t life to people on the Internet.
B)1)Now all you need to be famous is the Internet.
2)They were making videos of themselves singing or acting as a Star Wars hero and put them on YouTube.
3)Yes,I've heard of many web celebrities . They just make videos of their lives which are called vlogs and put them on YouTube in order to show their lives to the audience of millions of people.