Best practice is: write all text that you want to convert to HTML. Now just select desired part of the text and click button that will format your text (for example button with letter A which changes text color).

If you want to make a link it's similar. Again select the text and click on the "chain" button. Now just fulfill all necesary fields in the popup form.

If the button is grayed out that means that you need to select text first.

Last 4 buttons in the 4th row are very helpful:

visit here: - http://html-color-codes.info/html-editor/