I think Rails or basic PHP are good places to start. There are plenty of screen-casts and tutorials out there for both. They may not go into depth, but they will help you learn the basics of web programming. You should move off of either once you are comfortable as there really is a huge ecosystem of web programming languages, frameworks, and practices and it will take some time to find the one you really like best. I am going to assume that you are not interested in the HTML, CSS, and JavaScript aspects of web programming at this time.
PHP is a good start because it is simple. It is fairly trivial to set up a quick LAMP (Linux-Apache-MySQL-PHP) server. The Ubuntu Server distribution even has a system configuration option for it in the installer. It's also very simple and easy to create a minimal dynamic page such as one that stores the data from a form in a database and displays it, or does some minor calculations. The ease of set up and the ability to just plop some <?php ?> tags in HTML are PHPs real strengths for the beginner. PHP does not lend itself to large applications without careful thought and experience with organization.
Ruby on Rails is a decent framework for the beginner because it is so opinionated and will do a lot of the defaults for you. You will likely generate a few models and scaffolds and can fill in the gaps with your application logic. It is a lot more complex than just starting with PHP, particularly in terms of integrating with a real web server. The benefit is the opinionated programming and sensible defaults. Having the framework make some good guesses for you frees you from having to make every little decision before you understand it. As you get better at the framework you will realize why these defaults are so sensible and you will learn a style of web programming that many smart people have worked to refine. The major limitation will be that it can be hard to do things that the framework didn't expect, and writing your own plugins is leap in complexity from setting up simple apps.
In short, PHP is very easy to set up for simple pages, but quickly gets cumbersome without experience as the size of the application grows. Ruby on Rails is also easy to get started with, and will expose you to many good practices, but it provides a narrow path for development.
Start with one of those two, then try out whatever you think is cool once you know what all the buzzwords on their home page mean.
Comments
I think Rails or basic PHP are good places to start. There are plenty of screen-casts and tutorials out there for both. They may not go into depth, but they will help you learn the basics of web programming. You should move off of either once you are comfortable as there really is a huge ecosystem of web programming languages, frameworks, and practices and it will take some time to find the one you really like best. I am going to assume that you are not interested in the HTML, CSS, and JavaScript aspects of web programming at this time.
PHP is a good start because it is simple. It is fairly trivial to set up a quick LAMP (Linux-Apache-MySQL-PHP) server. The Ubuntu Server distribution even has a system configuration option for it in the installer. It's also very simple and easy to create a minimal dynamic page such as one that stores the data from a form in a database and displays it, or does some minor calculations. The ease of set up and the ability to just plop some <?php ?> tags in HTML are PHPs real strengths for the beginner. PHP does not lend itself to large applications without careful thought and experience with organization.
Ruby on Rails is a decent framework for the beginner because it is so opinionated and will do a lot of the defaults for you. You will likely generate a few models and scaffolds and can fill in the gaps with your application logic. It is a lot more complex than just starting with PHP, particularly in terms of integrating with a real web server. The benefit is the opinionated programming and sensible defaults. Having the framework make some good guesses for you frees you from having to make every little decision before you understand it. As you get better at the framework you will realize why these defaults are so sensible and you will learn a style of web programming that many smart people have worked to refine. The major limitation will be that it can be hard to do things that the framework didn't expect, and writing your own plugins is leap in complexity from setting up simple apps.
In short, PHP is very easy to set up for simple pages, but quickly gets cumbersome without experience as the size of the application grows. Ruby on Rails is also easy to get started with, and will expose you to many good practices, but it provides a narrow path for development.
Start with one of those two, then try out whatever you think is cool once you know what all the buzzwords on their home page mean.