Some dislike w3schools if you are not already familiar with things. I am not sure I would go that far. If you intend to become the all knowing web coding reference manual then I would not suggest there but if you want to get stuff done then you could do far far worse.
For Javascript I would suggest
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Introduction and others would probably point at the mozilla developer network for other things.
"All I know is that I should probably learn HTML first and then maybe move on to CSS afterwards"
Then you know/were told wrong. HTML and CSS in the so intertwined in the modern world it is basically impossible to separate them. If you want to stick to the older versions of HTML (don't do that) then you might be able to put off CSS for a tiny bit but not for long.
On getting HTML+CSS on lock and then going to php... can't get behind that one. PHP is probably one of the quickest actual programming languages to learn and get by with and you could do a lot at the same time. Now this is also dangerous as php will still give you enough rope to hang yourself, especially if you are trying for security (do you know what a unique per user salted hash table is and why you would want one? No, that is OK as php will allow you to put something public facing without it). Oh and the only valid security that javascript can provide is that crawler bots usually do not like it -- it runs on your attacker's computer so clearly nothing it does could really be trusted.
On SQL. Just make sure you understand roughly what you are doing and make sure your queries are about as nice as they can be to the database and you will do OK. Do also remember the SQL might not be the on the same server as the php interpreter and that counts for something. Do also read up on SQL injection, it has started to go away but I still see some newer developers making the mistakes.
As always if you have a project to keep you entertained then great, if not then I suggest having some existing piece of code and seeing if you can trace down things within it -- one thing I often find is I speak to a nice new HTML+CSS+PHP dev that will almost be able to make me a site from scratch from memory of the commands but you send them into a client site that has a wordpress install that has been customised over the years (possibly badly and usually with little regard to child themes or forking a plugin) and watch the panic attack form. Or if you prefer then get an average theme for wordpress (one of the slightly older twentytwelve/twentythirteen type ones) and change the width? Your nice w3 schools education has taught you to make a nice div and assign it a width, technically that was done here as well but have fun hunting things down. However this is why we have
http://getfirebug.com/
If you lack toy hosting somewhere online then I highly suggest a copy of
http://www.uniformserver.com/
I can not offer much guidance on ruby on rails, ASP.net or mssql. If you want to learn one kind of code related thing that is not html, css, javascript, php or ?sql then I suggest
https://httpd.apache.org/docs/2.4/howto/htaccess.html time was it might have been XML but I think JSON has damaged that position somewhat, though knowing your way around XML is not a bad plan.
Oh and it is not strictly web coding but I do also like to link things like
http://www.designmantic.com/blog/wp-content/uploads/2014/05/Color-Theory-Infographic.jpg and
http://www.designmantic.com/blog/wp-content/uploads/2014/04/font-infography.jpg at these points in time.
Also if you plan to do this for other people then
http://theoatmeal.com/comics/design_hell
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