You defenetley need a database and a language to create the application/script. Your first decision is to choose what language you want, then the database. The 3 different languages I recommend is PHP, Java or .NET (C#). When you have decided what language to use it is time for the database. If you choose to use .NET you should use MSSQL, microsofts database. If you choose any other language you probably want MySQL or Postgree SQL.
When you start you should start out small, making for example a list of your DVDs. When that is up and running extend it to contain the cast list. Continue to create small stuff like this until you feel comfortable doing this.
Now it is time to design your application. Design the database and GUI, then design the application in between. It will take some time, but it is time well spent. When I started I skipped this part, and often had to do everything 2-3 times before I got it right. After you have a design it is time to start coding.
There is one part you should not handle yourself. The actual handling of money should be done by an external site, for example PayPal.
And last a warning: Make sure your code are safe against SQL injection. It is a way for someone to be able to get information from your database they should not be able to get, or even change or delete things.
Happy learning and happy coding 🙂