How to protect MySQL database from sql-injection? I am new to databases and security.  

I am planning to put up a website. 

I've read that sql-injection vulnerabilities can be very dangerous since the server might leak user passwords and credit-card information. 

Are there any steps that I need to follow to prevent SQL injection vulnerabilities?

I was going through a wiki on sql-injection, but I didn't understood the following query:

SELECT * FROM users WHERE name = '" + userName + "';
you better use prepared statement from your programming source code, e.g. for PHP use PDO's prepare statement!

Check this - https://stackoverflow.com/questions/60174/best-way-to-prevent-sql-injection-in-php