Where to even start? Front-end languages would be HTML(5), CSS(3), JavaScript, jQuery only after understanding JavaScript, and PHP (along with MySQL [PDO specifically as it translates across all database platforms such as Oracle]). HTML is the structure of a web document. CSS is for looks, layout, colors, etc. PHP, while server-side (back-end), works behind the scenes to make powerful, dynamic websites. Your browser processes HTML and CSS. PHP is processed on the server. A server is the machine that hosts the website files. This can be your own computer or in a massive server room somewhere across the country. Your computer requests the document, located at a specific IP address but usually named something like website.com, and using HTTP files are sent back to your computer from the server and put together.
For databases, you need MySQL (PDO specifically) along with most typically PHP.
Not sure what you mean when you ask what if you want to build apps that use those databases.
I don't know anything about Ruby, but PHP can output database information in many ways. JavaScript and jQuery manipulate elements or data to produce effects or changes to those elements.
Most well-known web hosts should be able to handle any language you mentioned (again, I don't know about Ruby so not sure) but email support if you want to know for sure. I've used Dreamhost and I know they handle html, css, js, jquery, php and mysql databases just fine.
Most of the rest of your questions are best answered by someone else. I'm pretty new to all of this but I've learned all that I mentioned and more in a year's time.
Start with codecademy to get your feet wet. Learn all the basics there and start building websites now. It's intimidating but I taught my 5 year old son how to make a website in about 10 minutes. Simply <html>My website!</html>. It's a bit more than that but that in and of itself would work.
Check out the page source of websites. It's fantastic learning information.
Download Sublime text editor, MAMP if you use a Mac or WinAMP if you use Windows.
That's about all I got in me; I may add more later. But the earlier you start building the better.