When creating content in Canvas, you can use the Rich Content Editor, a WYSIWYG (i.e., what you see is what you get) editor for text, images, audio, and video. You can also use the Content Selector to insert files, images, or link to content, tools, and assignments already in your course or uploaded from your computer.
Instructure Guides:
Of course, some tasks (like inserting embed code) require an HTML Editor. The link that toggles from the Rich Content Editor to the HTML Editor is to the upper right. Check out the Canvas Guide about HTML view, or go straight to the Canvas HTML Allowlist.