GitLab CI/CD is a part of GitLab, a web application with an API that stores its state in a database. It manages projects/builds and provides a nice user interface, besides all the features of GitLab. GitLab Runner is an application which processes builds.
Who Needs CI/CD Pipelines?
Organizations looking to automate the build-test-deploy process of their software development.
Why is CI/CD Pipelines Important?
It is important to have a repeatable process. When you push code to version control, that code should be tested and deployed automatically through Dev, Test, QA and Prod (depending on how your organization is set-up one or more of these environments may not exist).