Lists are used whenever you have a group of related items - navigation menus, feature lists, step-by-step instructions. In Salesforce, think of things like picklist values, related records, or sidebar menus.
<ul> creates a bullet list (unordered). <ol> creates a numbered list (ordered). In both cases, each item goes inside an <li> tag:
<ul>
<li>Sales Cloud</li>
<li>Service Cloud</li>
<li>Marketing Cloud</li>
</ul><ol>
<li>Create the Apex class</li>
<li>Write the test class</li>
<li>Deploy to production</li>
</ol>The first one shows bullets, the second shows numbers. I always confuse which is which - ul stands for "unordered list" (bullets), ol for "ordered list" (numbers).
You could technically stack divs to create a list, but <ul> and <ol> give you built-in bullets or numbering, and they tell the browser "this is a list of related items." Screen readers announce them as lists, which helps accessibility. In LWC, when you iterate over data to display a list of records, you'll typically render each record as an <li> or a <div> depending on the layout.