Choose the highlighter tool and then select the text. You can also first select the text and then click the highlighter tool.
Click on the highlighted text and then click the trash icon.
Click the + button next to your highlight to add a comment. Highlights with a comment will have an outline on them
Add emojis to your comments by clicking on the emoji button in the comments section
Change the color of your highlights by clicking on the paintbrush icon next to your highlight. Click to cycle through possible colors.