What is your current way?
Jars are library’s byte code ready to be used in your code. For example, Processing libs are found in the core.jar which is part of the Processing distribution, right when you download Processing from the website. For non-Processing libraries, you need to make sure those libraries are accessible by your code. If you build your own code, you will use the classpath flag. If you are using Processing to run your code, then you need to include the jar in your sketch. The easiest way is to drag and drop the jar right into the Processing editor. This will create a folder called code at the same level as your data folder. This code folder will contain the jar file(s) and they will be including during the building process for you. To access those function, you need to explicitly make those resources available via import statements, for instance import com.some.external.library.
You might find this next useful: http://happycoding.io/tutorials/processing/libraries
Kf