w is one of the Japanese Internet slang, which means lol or Lol in the U.S.
It originally came from "2channel", the largest textbord in Japan, and so only "otaku" used w. Today, however, many people who are not heavy Internet users also tend to use w as lol.
What is interesting is that it means not only "pure laugh" but also self-deprecation, like "I failed all my classes wwwwwwwww. The end of the world wwww"
More ww simply means more laugh in many cases, but not necessarily.
Does it make sense? Hope it helps you :)