Hi @MelanieGann,
Welcome to the Instructure Community, glad ot have you here!
In my opinion, your question probabl needs more input from your teacher/professor than anything.
If you're typing your assignment directly into a Canvas textbox, that is what would be considered web/html format. Formatting for the web (where every user's computer will display things differently based on their window/screen size) is a lot different than typing for print where you have a designated paper size, margins, etc... That is one of the reasons you don't really see as many options for online editors compared to a program like Microsoft Word (no double spacing, hanging indents, etc). You can usually accomplish formatting changes for web content too, but it will usually take some knowledge of HTML code and is not as easy as clicking a button. The Create Hanging Indents Using HTML and CSS | Resilient Educator article describes how to create hanging indents with html, though in the beginning it even says, "While, strictly speaking, hanging indents are a part of correct APA style for footnote references, it is worth noting that the use of hanging indents is often considered unnecessary for footnote references appearing online versus in print. Given the shift away from hanging indents for things like footnote references in an online environment, the real question may not be how to add hanging indents into your content, but whether they are really necessary for the purposes of your content in the first place."
If your teacher/professor insists on double spaced format with hanging indents, the easiest thing for you to do would be to upload a word doc instead of trying to type in the Canvas editor directly. If that's not an option for your assignment, I think your teacher is going to need to give a lot more guidance on what they want and how they want all of the students to do it.
I hope this at least helps start a conversation.
-Chris