• <!-- and --> are for commenting in the code. you should do this. keep it clean, legible, and make sure you label what different parts of the code actually do.
• <strong> and <em> contain metadata that browsers and screenreaders use, so are generally always what you want. <b> and <i> display the same but don't contain any other information. You usually want the former unless you specifically only intend to change appearance.
• you use "../" to go up a directory. you start a path from the folder your current page is in.
• for example, in the same directory you'd simply type <a href=file.html>
• if you're in root/folder1, and you want root/folder1/folder2/file.html, you'd type <a href=folder2/file.html>.
• if you're in root/folder1 and want root/folderA/file.html, that's <a href=../folderA/file.html>
• you use html entities to display reserved characters as plaintext. for example &amp; for &, &lt; for <, or &gt; for >
• wrap a link tag around an image to make the image a link. you can use alt= for alt text. title= for hovertext on links (which can also be images)
• you can use "id=" to do all sorts of stuff by giving a part of a page a special ID. These are unique, only one thing should have an id. you can link to it in the filepath. like: <a href=folder2/html.text#Section3>, or just #section3 if it's on the same page.
• You can add target="_blank" to a link to make it open in a new tab.
• make descriptive lists with wrapped dl tags. terms are dt, descriptions are dd.
• sup and sub for superscript and subscript
• pre for a section keeping whitespace as appears in editor. "br /" for a linebreak