I'm just starting and lost

Hi there! I believe you're referring to this challenge. And indeed, working with stylesheets was at least briefly looked at around 2:12 of this video. You will see Treasure moving back and forth between the index.html and styles.css.

The challenge starts you with an index.html and a blank styles.css. It is empty because it only wants one rule written there, and that's the rule you're to write for the challenge. On step 2 you're asked to change the color of the h1 tag to purple. So I'm going to show you an example, and I think you can extrapolate from that exactly what they're wanting.

p {
   color:  red;
}

This will change any paragraphs' font color to red. We start with a selector then enclose our rules inside curly braces. Each rule should end with a semicolon.

In this particular challenge, there should be a preview available. You should have "Restart", "Preview", "Get help", and "Check Work" button. If you're not seeing one of these, it should probably be reported to support. When you press "Preview" it will change to "Editor". This is simply a toggle for the "mode" that you're in. That being said, you might have to toggle a couple of times to see the difference. This is rare, but has happened to me before.

Going forward into the challenges, it's important to note that some challenges will be very similar to the projects that you're working on while others are going to be quite different. But the "big ideas"/"main concepts" will be the same. In some challenges you will have an opportunity to preview your work. In others, this will not be available. Try and follow the instructions to the letter and try not to do anything the challenges don't explicitly ask for. Even if functional outside the challenge, it can cause the challenge to fail as it no longer meets the strict requirements.

Hope this helps!