I'm starting to study the Van-Kampen Theorem and I realized there are some questions we can use this theorem directly. I find this theorem difficult for a beginner. Do some of you know some questions which can be solved directly using The Van-Kampen theorem? I think it's important to have examples for beginners.
There is a similar question here: Good exercises to do/examples to illustrate Seifert - Van Kampen Theorem. In spite of the title, the question was more about the understanding of the author of the concept of this theorem than the examples themselves, and almost every answer was focused in this part.