If you have a project on GitHub, chances are you will want to continually build it to ensure it is still compiling, that it is still working — meaning, all tests are passing — and possibly create a release of the project so others, including yourself, can simply use the latest version without having to manually compile/package it. For all that, you will need a build pipeline.
GitHub now has a feature called GitHub Actions that can be used for many things, especially workflows that are triggered by events in your repository — like "issue created" or "push." And while developers can be very creative and extrapolate the boundaries of what GitHub Actions is aiming for, the reality is that for complex applications continuous integration and delivery, you are more likely better off with a platform that gives you control over build agents, software provisioned in them, custom webhooks, human control over workflows, and so on.