The CSS box model is essentially a box that wraps around every HTML element.
It consists of (from innermost part to outermost part): content, padding, border, and margin.
Web Design with HTML5 and CSS by Alec Fehl
There are many code editors available. Some are free while others are commercial products you need to buy. Regardless of which editor you choose to use, you need to figure out how to set some code options. Here are a few you're probably going to need to know how to change:
© ♥This is a test page....
You'll also need to make sure your editor either supports spell checking or supports extensions so that you can install a spell checker. Misspelled words on a client's website can destroy their professional credability, which in turn destroyes yours.