A very concrete approach to modular forms.
You needd to have docker installed in your machine. Then, pull the docker with
docker pull sagemath/sagemath
and run it as jupyter notebook from the root foldedr by
docker run -v "${PWD}:/home/sage/volume" -p8889:8888 sagemath/sagemath:latest sage-jupyter
Visit http://localhost:8889 to start playing with the notebook (you will find it in the /volume folder). Also, check your terminal to get the token!
Once you have run the SageMath docker, simply run the notebook from the browser.
The notebook is structured to be read from top to bottom, but you can also jump directly to the section of interest.
I do not claim anything on the algorithms: they are standard tools in SageMath. My effort is to bring together the main ideas via examples and intuitive reasoning.
If you think there are missing sections or some explanations are simply not well written (or wrong!), please let me know!