The rules for the String Calculator kata get steadily more complex. So, creating a great solution for this works well with the concept of Agile development, using TDD. The idea being that you add one rule at a time, use refactoring to adapt your algorithm and support the new behaviour.
In real life, you will often work on a project, then come back to it months later to make a change for your client. When working this kata, don't think of each rule as a sequence that you are working on in an afternoon or evening, think of them as new instructions that are separated by months and that have arrived in separate briefings from the client.
By the end of this kata you will really have built a great foundation knowledge on how to work TDD.
Getting set up can be the roadblock to starting a kata. In our screenkatas you can join our Software Craftspeople and let them show you how to set up your repositories for Java, PHP, Python and Typescript. For other languages, check out our guide on GitHub.