The Insert tab displays all the options for you to add content. You can add new text boxes, images, or input files from your Google Drive. You can also modify the layout of each page.
Options for how to modify your text will depend on which label you give it: normal text (default), title, heading, subheading, small. Once you select a label, you will be able to see options to align, bolden, italicize, bullet-point, hyperlink, etc.
Hyperlinking will only work if your text is labeled Normal text.
Any time you insert something new (text, images, from your Drive), the default is that it will appear on the bottom of your web page. You can drag it up and down the page by moving your mouse over it until you see the 10 dots appear on the left side or top of the item. Hold on to the dots and drag the item to where you want.
The Embed tool essentially embeds a webpage into your webpage. I discourage you from doing this because this tool is still clunky, and it will clutter your web pages. Instead, use a hyperlink.
All other items are either a different way to do the same thing or they involve similar steps. Just try to insert a few various objects to see what it looks like. You can always delete mistakes by clicking on them and pressing the trash icon ;).