You can add a jar in Eclipse by right-clicking on the project and then click on the Build Path -> Configure Build Path. Under the Libraries tab, click Add Jars or Add External JARs and give the Jar. For reference, you can have a look at this video.
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The above solution is a "Quick" one. Also, keep in mind that while you are working on a project where you need to commit files to the source control repository, I would recommend adding Jar files to a dedicated library folder within your source control repository and referencing a few or all of them as mentioned above.