Where to place .jar file in extensions making

[Ken]

How to Add Path of a External Library [.jar] to Build.xml

As I’m new to extension development. I was searching for how to add external library and I found this https://docs.google.com/document/d/1xk9dMfczvjbbwD-wMsr-ffqkTlE3ga0ocCE1KOb2wvw/pub#h.3kn0fmfydnq1 But It is so confusing for me, please can anyone help with any other documentation.