Continuous integration (CI) and continuous delivery (CD) (eventually deployment) are the processes that are used to build, package, and deploy your application.
Here is a diagram depicting the flow of CI/CD:
Essentially, the developer team commits the source code to a version control system—hopefully a GitHub repository; the CI tool polls down the latest version of the code and builds the application.
Building also involves unit testing and integration testing. There are different frameworks out there to use for both unit and integration testing. Of course, it depends on your runtime environment. For example, in Java, you can rely on JUnit and Arquillian for unit testing and integration testing, respectively.
The build phase also includes code inspection for quality, spotting anti patterns, optimizations, coverage, style...