If you have portforwarded successfully fill out the blanks:
Target Server -> Server IP were you want to have op/gamemode ...
Target Port -> Port of the server
Messages -> you can chosse whaqt you want to do eg. op yourself (op yourign) or change you gamemdoe (gamemode yourign) or stop the server (stop) ...
MOTD -> Message of the day doesn't matter leave it blank if you want
Users Online -> fake number of users online eg 23
Max Users Online -> fake number of maximum members online eg 50
Listen Port -> The port you have forwarded eg 25565