I am confused about the pseudo tags

You're using the correct wording and not nag?

/* links */
a {
  color: blue;
}

/* nav link */
nav a, nav a:hover {
  color: red;
}

no I'm using nav... nav a, nav a:hover { ^^ why do I have to declare nav a, nav a:hover and not just nav a:hover...

Essentially you're selecting two elements and applying the same styling to them in your code here.

"nav a" is selecting the anchor elements on your navigation while "nav a:hover" is selecting them when your mouse is hovering over the link. If you are applying the same styling you will not see any chenges when you hover over the links in your navigation. Most often people style these different by bolding, underlining or changing the color of the link when a mouse hovers over it to indicate to the user that they're interacting with the web page.

Technically you don't have to declare each individually if you don't want the styling to change. However, if you DO want the styling to change you will need to declare separate styles for each scenario (regular link in the nav and links in the nav when hovered over). You would do this by splitting them up.

In the code below, all of my links would default to blue. My navigation links would then be overrwritten and show as red (only nav links). Then, when a mouse hovered over a nav link it would be red but then become bold as well.

/* links */
a {
  color: blue;
}

/* nav link */
nav a {
  color: red;
}

nav a:hover {
  font-weight: bold;
}