For a while, I have been thinking about creating my own WordPress themes, but I didn’t know where to start or how many hours it would take. I always assumed that it would take many hours and that I would have to create templates, style sheets and more for a number of pages. In reality, you need an index.php page and a stylesheet. Anything else is a bonus.
A shortcut is to find a theme that you like and to see which fields you want to modify and just modify that behaviour. Choosing to use another font requires one or two lines of code. With minimal effort, you can personalise a theme.
The course I watched is “WordPress: Building Child Themes” and within two hours you will see how to use CSS, functions and templates to change one or more aspects, using the themes that you select. Personalising your own theme, can take seconds rather than hours.
It also gives you an opportunity to learn with a small challenge, and as you grow more confident you can try more and more ambitious projects.
You have the Theme Developer Handbook to help you along.
What I would like to do is find a way to create themes by subject for pages so that I can make my website fully dynamic, and bring the static pages into the 21st century. This will require some trial and error, hence the value in playing and experimenting, until it works.