Read the SPI Overview and Functions documentation.
# if mac os
% export JAVA_HOME=`/System/Library/Frameworks/JavaVM.framework/Versions/A/Commands/java_home -v "1.8"`
% ./mvnw clean compile package
Copy jar file to plugin dir. And, you restart presto server.
% mkdir /usr/lib/presto/lib/plugin/hello/
% cp target/presto-sample-udf-1.0-SNAPSHOT.jar /usr/lib/presto/lib/plugin/hello/
% /usr/lib/presto/bin/launcher restart