Step : 1
Download JAR or AAR or both file into your computer or laptop.
Step : 2 (In case of AAR)
Change the file extension from .aar to .zip and open zip file and extract .jar file.
Step : 3
Past your .jar and .aar file into lib folder.
path is : appinventor-sources/appinventor/lib
Step : 4
Add path of external libraries into build.xml file.
Path is : appinventor-sources/appinventor/components/build.xml
Reference : see this
Step : 5
Add @UsesLibraries annotation into your code.
Example : @UsesLibraries(libraries = "example1.jar," + "example2.jar")
Reference: see this