How can I learn what I need to know about HTML, CSS, forms, and accessibility as quickly as possible?

Logistical question: As someone starting from scratch with HTLM, CSS, and Forms, I'm really struggling to read all the webpages linked, complete the tutorials, and retain information. Could you go over what are the most important resources to look over? 

What is the difference between ""placeholder"" and ""value"" in forms?

Is there any consequence with LABEL using ID not being able to "wrap"/surround the input?

Are labels ever used for reasons other than for screen readers/assistive technology?

When you submit something via a form, where exactly does this information go (does it always go somewhere?) Do you have to specify a location to use a form?

Is there a way to run get requests from the browser?

Can you please go over the structure of GET vs POST