Build (the same in .travis.yml):
mkdir bin
javac -d bin $(find src -name *.java)
jar cfe checkers.jar Checkers -C src .
Run:
java -jar checkers.jar &
You should see:
Run it again to have two windows, click "Stwórz grę" (Create a game) in one of them.
Then go to the other window and click "Dołącz do gry" (Join a game). Dialog will appear asking you for server IP address - leave the default (127.0.0.1) and press OK.
A game should start:
