WordPress 101
There are many many tutorials out there that will go through the various stages of building a theme. This is the one that Fabiana found useful in her MP journey and it might help you too ツ
One word of caution from me before you dive in:
Be aware that this tutorial quite literally starts from scratch. Alessandro explains all the functions and you will learn a lot. However, do not assume that you can only view some parts of this tutorial series and be able to have a full-fledged theme in hand. You will need more than the first few files for a complete theme.
If you find this a useful way to learn, make sure to see it through and do complete all the parts which will then give you the full set of files for your theme. Only once you’ve worked your way through the series will you have all the files you need.
My tutorial
The reason why my tutorial does not take this drastic approach is the time limit. As we only have the one day’s workshop, this method would not have worked for us as we would have run out of time. The aim of my tutorial approach was to ensure that you will have one full theme completed and that we have gone through all the steps required from prototype design to theme once. Bonus being that you’d have essentially 2 themes to start your own theme build with.
My Vanilla theme includes all the files you will need to start with. Even some you might not. This means as a starting point, your theme folder is complete bar your own edits. It is a bare minimum set of files but complete ~ meaning if you publish a page, or a post, all required files are included and will allow you to finalise your design.
My advice:
The WordPress 101 tutorial is excellent to learn more about all the specifics of a theme build. As time can get tight, the quicker way to get your theme done will be my Vanilla theme as starter theme and edit the files to suit your design. You will work with the functions as included and learn how to use them by doing your edits. This will make you more familiar with the code of the theme files and using the DevTools to inspect the given code will allow you to understand how to make any changes you need.
Once you’ve done your own theme build, have time without deadlines and if you are planning to become a proficient WP developer, then the WordPress 101 will be an excellent next step to learning more and diving in deeper.
UPDATE Jun 2025:
Take a look at this post which includes links to 2 excellent resources ツ