What will happen when the star Betelgeuse goes supernova?

It will explode. As Betelgeuse is only about 650 light years away, it is more than likely that it will be visible during the day and outshine the Moon at night.

Contrary to "internet" belief it will not destroy the Earth with it's gamma ray burst, as it's rotational axis is not pointed towards us.

It may be seen anytime soon, astronomically speaking.