i put on the launcher play then it says donwload then it says crashed

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
minecraft would start and I would play
What actually happened was...:
Describe what happened here
I put play and it crashed
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...