This is a list of minimum information needed in order to determine what is wrong with Cura.
Not sure which operating system you are using? http://whatsmyos.com/
Linux: Run this command in the terminal uname -a && cat /etc/*release
Mac OSX: https://support.apple.com/en-us/HT201260
Microsoft Windows: http://windows.microsoft.com/en-US/windows/which-operating-system
One example being v17.10
If you are able to launch Cura, check the title bar at the top.
If Cura is unable to run, check the installation file which is usually saved in your downloads folder or on the desktop.
What does it take to experience the problem?
If the problem is not repeatable, what other potentially related information can you provide?
What do you anticipate happening when you do the above steps?
What does happen? What goes wrong?
Does the application give an error message? What is the exact text that it displays?
Does the problem only occur with certain files? Are you able to provide these files publicly, privately, or not at all?
Do other versions of Cura work?
Have you tried on a different computer or operating system?
Can you still accomplish your goal through another mechanism?
Then follow these instructions to actually submit the bug report: https://code.alephobjects.com/w/submit_a_bug_report/