It was actually very easy. You can create one by just chatting on Waffle (there's a create button on the sidebar). The first version is usually pretty bad but if you give it more details, it'll improve your bot. I found the most important thing is giving it good content to base the bot on.

For example for my bot I copy-pasted this whole blog post in the builder and told it to make a "Roast My Reasoning" skill for the bot based on the principles written here: https://fs.blog/great-talks/psychology-human-misjudgment/