Hello @jonathan,
Summary:
Creating a font involves a good understanding of typography and the tools used to manipulate it.
Image Credits: FontLab Studios
Why design a custom font?:
As a part of the Hashnode rebranding, I created the font for the Hashnode logo from scratch using the principles of geometry and symmetry.

Here are some of the questions I asked myself:
- Why design a new font?
A fundamental question to ask yourself before designing a font is "why?". There are thousands of fonts to choose from. Is your font going to solve a problem? Where is your font going to be used most? Who is it going to be used by?
- What fonts inspire you?
Look at some of the fonts that inspire you and/or your design. Understand their anatomy, and learn from them.
- Is the font going to be 'Serif' or 'Sans-Serif'?
Understand the differences, and select a category according to the intent of designing your font. For example, if you're designing for print, then consider making it a Serif font because of improved legibility.
(See also Serif vs Sans-Serif)
- Are you creating a 'font' or a 'typeface'?
Creating your own 'typeface' requires a lot of time and resources. Once you understand why you are designing your own font, you will have the answer to this question.
(See also Fonts vs Typefaces)
- Design for optimal legibility and readability?
Learn the basics of legibility and readability and apply them to your design.
(See also Legibility, Readability, and Comprehension)
Useful resources:
- Adobe Illustrator (Mac OS and Windows)
Industry-standard vector editing tool.
www.adobe.com/in/products/illustrator
- FontLab Studio (Mac OS and Windows)
Font editor for font professionals
www.old.fontlab.com/font-editor/fontlab-studio/
- Anatomy of Typography (Article)
Understand the essentials of typography.
www.designersinsights.com/designer-resources/anatomy-of-typography
- How to create your own font: 18 top tips (Article)
A guide to creating your own font.
www.creativebloq.com/typography/design-your-own-typeface-8133919
- Prototypo (Web tool)
Quick, but limited,tool for generating a custom fonts.
Suggested by @hipkiss91
www.prototypo.io