https://typedesignresources.com

Designing Type by Karen Cheng is an incredible reference, but its not exactly the best way to get started designing your own type IMO. I'd suggest Designing Fonts by Chris Campe & Ulrike Rausch. It's much more of a practical guide and takes you all the way through the type design process from ideation to sketching to vector drawing and letter spacing.
I also found The Stroke: Theory Of Writing by Gerrit Noordzij really helpful for conceptually understanding how to construct letters.

In addition to Cheng and Beier, get Bergsland Practical Font Design and fontmaking software (such as FontLabs). Have fun! If you want to get fancy, check out TypeDrawers, and The OpenType Cookbook.