Html code that makes everyone use a password to login your website?

[Agent]

Unfortunately, you can't do this through HTML.

You can create a basic login system using Javascript (however they're not secure and shouldn't be used for a website open to the public). An example of this is here: http://www.javascriptkit.com/script/scri...ass2.shtml

You need to learn a language like PHP or ASP. Personally I recommend PHP, it's more widely used (Google, Facebook, Yahoo, Wikipedia and Wordpress all use PHP), compared to ASP, which seems to mainly be used by Microsoft owned companies (which makes sense, since Microsoft created ASP). The main important factor in this case is cost. PHP is free and open-source, whereas ASP is not. If you were certain you could make significant money with your website, you could go with ASP, but the benefits are not worth it in my opinion.

Javascript is also very useful for websites like the one you suggest.

Lastly, you'll need to know a database query language like MySQL or MSSQL. MySQL is the free, open-source one, and MSSQL is the commercial one that you have to pay for made by Microsoft.
MySQL is more widely used, just like PHP. This means that for both MySQL and PHP, there will be more support and examples online that you can learn from and get help.