There are ways to manually create a hanging indent, but you should always go for the built-in tool if it's available* (and it usually is). You'll want to look for paragraph settings relating to indentation.
These instructions are for Google Docs accessed in a browser (desktop). The app (mobile) does not provide this function. If you are using the app, you can do the otherwise not-recommended method of manually creating the hanging indent by creating line breaks yourself, then tabbing each line over…. but the desktop method described below is superior. The Google Doc can display hanging indents in the app, so you could edit your document on a library computer if needed to quickly apply this formatting.
In your document, highlight your citation(s) to select them, then go to Format > Align & indent > Indentation options.
In the Indentation options window that pops up, select "hanging" under Special Indent. Make sure it says "0.5" in the field next to that dropdown, then click Apply.
Voila! You should have a lovely (or several lovely) citation(s) with the indentation.
*Why?
- It's ultimately faster -- the tool can do all your citations at once.
- It's more accurate because it takes care of the alignment for you.
- If you have to edit your citation, you won't have to redo any of the line breaks -- your citation will grow/shrink but still flow in the hanging indent shape.