Minecraft keeps shutting down when i try to try it i want to get it but if this happens when i buy the real version its going to be a waste of good money

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here it shuts down almost immediately after I hit play demo world

Steps to Reproduce:
1. Log in
2. ...hit play demo
3. ...hit play demo world and it freezes