Since Moodle version 2.7, there's a simple interface for entering text that is for forum posts only.
The thinking behind this change is that users are looking to enter text just as they do when they're using Facebook or other social media. You can use standard keyboard shortcuts for simple formatting (bold, italic, and underline), but for any embellishments beyond that (inserting links or images, adding bullets, creating a table, etc.), you need to select the advanced editor. Once you open this editor, you'll be able to use all of the formatting options available in our normal HTML editor as shown below.
CAUTION: If you begin to draft your response and then decide that you need to use the advanced editor, copy what you have already written (using Ctrl+C or Command+C) BEFORE activating the advanced editor. When you switch to the advanced editor, anything you have written in the text box will be wiped out. (Moodle will generate an alert that the text will be lost if you continue, so you do have a chance to stop and capture your work.) Use Ctrl+V or Command+V to paste what you copied into the new text box. Be sure to share this information with your students as a reminder.