Generally, there are three cases of game crashes:

• Launcher Crash:
  
  • If the standard Launcher is used, report to the game devs directly.
  • If BLSE is used, check for BLSE_lasterror.log in the folder where BLSE is installed. Report it in BLSE's mod page.
    

• Game Standard Crash (The application faced a problem): follow these instructions
  

• ButterLib's Crash Report: follow these instructions.
  • If you know what mod is responsible for the crash, report it in the Bugs section if it's available.
  • If you don't know the mod that is responsible for the crash, check out the Involved Modules section in the crash report!