Both links above, W3Schools and W3.org, are incredibly useful resources but have different strengths. W3Schools is a very simple format and organized efficiently, but only offers so much information depending on the clicked page. W3.org is very detailed and includes many useful steps, but this can be overwhelming.
I find both to be helpful in different ways and I encourage others to try both of them at least once.
While I am still learning I'm enjoying myself so far with the current projects. Especially when I found a way to reach my URLs for my projects. For some reason I have to add a %20Folder to be able to reach my items. While I haven't looked into this I'm sure there's a logical explanation.