Continuous Integration - a practical approach

When programmers work together on the same code, they need to ensure that they are working with the same code base and that no version conflicts occur. When developing software according to the "Agile" methodology, code is added in many small iterations into the final product (a software package or web application).
How do you make sure this all goes smoothly and easily?

Peter talks about software development, the OTAP development process, collaboration, Continuous Integration, Git Flow, Git/Webhooks and issues he ran into.