The core element of a stack is a Pipeline. Each stack contains a template of a pipeline and a sample of variables. (example Stack magento pipeline template).
A pipeline describes the workflow of a stack, how to create the application and also how to automate and orchestrate the deployment of new releases.
When you create a project from a stack, the template is read by Cycloid to create a running pipeline.
It's important to understand the difference between a pipeline template and a running pipeline:
The template of a pipeline is contained in the stack repository. This template is used only when you create an environment. Which means, if you edit the pipeline using the Dashboard, you actually edit the running pipeline created from the template. Not the template itself.
Which also means, updating the template will not update the running pipelines that you have already created. See Refresh pipeline section to refresh your running pipeline using the latest version of the template.
Make sure to always keep in mind the difference between running pipeline and pipeline template described above.