Simple Quesiton: What is the difference between a regular file and a database?

I used to write CGI program that insert data into files. What I used to do was open the file, lock it, write to it, and then unlock it. If another user tries to insert something into the file while it's locked then tough luck. That's why I wrote a loop that would try writing to file a few times before quiting.

With MySql, I am inserting and updating data to the same database, but I have no idea how to resolve multiple users conflict. Is that done automatically?

What happens if two or more users try to insert into the database at the same time? What happens if they try to update a record at the same time?

Thank you.

i believe that mysql actions occur simultaneously, meaning that many users can be inserting data at the same time without a problem, and in the case of an update, the last action is the one that is stored