How to build a retaining wall?
+4
Suggested Project Book
Hope this helps you.
https://www.diynetwork.com/how-to/outdoors/hardscape/10-things-you-must-know-about-retaining-walls-pictures
https://m.youtube.com/watch?v=7bIdEXkJmOE#
https://www.constructionprotips.com/jobsite-tips/build-long-lasting-retaining-wall/
What materials would you prefer?
Granny and I spent some time gathering medium sized rocks and she turned them into a retaining wall by cementing them together.
If your wall exceeds 4' in height, you'll most likely be required to secure a permit through your municipal authority.