Here, are the key elements which you need to perfom the entire CI process:

• Version Control System (VCS): It offers a reliable method to centralize and preserve changes made to your project over time.
• Virtual Machine: You should have a spare server or at least one virtual machine to build your system.
• Hosted CI Tool Solutions: To avoid servers or virtual machines, you should go for hosted CI tool solutions. This tool helps in the maintenance of the whole process and offers easier scalability.
• Tools: If you select a self-hosted variant, you will need to install one of the many CI tools like Jenkins, TeamCity, Bamboo, GitLab, etc.

How Continuous integration work?

You are surely aware of the old phone Nokia. Nokia used to implement a procedure called nightly build. After multiple commits from diverse developers during the day, the software built every night. Since the software was built only once in a day, it's a huge pain to isolate, identify, and fix the errors in a large codebase.

Later, they adopted the Continuous Integration approach. The software was built and tested as soon as a developer committed code. If any error is detected, the respective developer can quickly fix the defect.