What, specifically, are you asking about? Are you asking about why it was dissolved from the top down and sold for parts to the west? Or is this about something more specific?

For clarity, the Soviet Union marked dramatic improvements for the lives of the Working Class, and showed that Socialism is a working economic model. Asking what went "wrong" without asking specifics helps nobody, the best answer to that is just directing you to Blackshirts and Reds, which took a critical look at what went right and what didn't in the Soviet Union and how it collapsed, along with the brutal reintroduction of Capitalism that killed 7 million people.