In simple words, CI is a software engineering practice where each check-in made by a developer is verified by either of the following:

Pull mechanism:- Executing an automated build at a scheduled time

Push mechanism:- Executing an automated build when changes are saved in the repository

This step is followed by executing a unit test against the latest changes available in the source code repository :-

Jenkins doesn’t need the introduction; it is an open source and one the most popular CI tools available in the market. It helps in automating the repetitive task of CI. Jenkins makes the process effective and transparent.