Prevent database from external access

I have created a home Apache server with MySQL and PHP. I have just created a website that I want to be publicly accessible, majorly for my experimenting. However I just realized that my MySQL server that is running on port 3306, usually my PHP connects to the database on localhost with a username and no password. Can't any other remote PHP script connect to my database and siphon off all the stored data? Does it not put my website in jeopardy? How do I stop remote connections to my database server? I only want the applications on my server(or those that I approve of), to access my database. Forgive me if the wording is bad, I couldn't find any helpful articles on Google.