Run client.exe to join (if server is open)
If on windows, run build.bat
If on linux, run linux_build.sh
If you want to run your own server for testing, create (or modify if you played before) a config.txt that looks like:
name=tkap1
ip=127.0.0.1
port=9417
color=a727ea
Then run server.exe, and then run client.exe (or start run.bat)
Find init_levels in shared.cpp
See how the other levels are done, do that
Make a pull request
You can press keypad ADD and keypad SUBTRACT to go up/down levels