orela .. Welcome to the forum. A search for Net Library would have revealed
Net Library v1.30
Extract the zip file and copy the .jar and .xml files to the B4a Install folder /Libraries.
Usually this is ... Program Files/Anywhere Software/Basic4android/Libraries. Restart your project.
Not all libraries come with B4a .. so maybe note you will have to do this again in the future.
Cheers mj