This video covers the display attributes and the values block, inline, and inline-block. One of the cool things that he does in this video is turning a bunch of <li> tags into a horizontal list, like a nav menu!
At this point, we start getting into some weirdness with CSS layouts. A "positioned" element is one that has display set to relative, absolute, or fixed. Absolutely positioned elements will only be positioned relative to the closest positioned ancestor, which I guarantee makes no sense right now, but we'll work through it!
Generally, if you want a fixed top navbar, you're going to want the z-index of that to be the highest on the page.
One catch that they may or not talk about is the difference between absolute and relative positions. I'd recommend checking out the documentation on the position style - in particular, the examples with the red squares do a pretty good job of showing the difference between absolute and relative.