well w3schools is basic tutorial and when you get what those basic codes mean move on to php.net and there a lot of codes but if you just go to php.net without knowing basic stuff in w3school you not going to know where to start learning
php.net provides all the functions with excellent descriptions of how they work. I use it every time I need a reminder of how a function works or what is available. As for a tutorial they don't really have that so i would check w3schools as KSclans says for that. Once you know the language though php.net will make a great reference
W3schools is the way to go, none of the ads are obstructive, there lessons are structured and to the point. They have a Try it editor to see a page instantly changed with your code, not much help learning PHP though. Php.net is great for reference.