500 Internal Server Error

Hi experts !
I have a form and when i clicked a button on my form to update my
Database an error occured like this:

500 Internal Server Error
If you are the administrator of this website, then please read this web
application’s log file and/or the web server’s log file to find out what
went wrong.

How can i fix my problem?how can i read my log file?
Thank you ver much