What should I do to get down to meet the mermaid? I pushed the rocks into the right box but nothing happened
Could be bugged. What version are you on? Try restarting the puzzle with button up North or leave and re-enter location.
If none of that helps you might be shit out of luck, JoiPlay-specific bugs are not exactly a priority.
What is the easiest job that give ok money? I know that i am very noob at fighting
If you're not already locked into Tough personality, you can try prostitution.
Getting 10 SUR and making Dry Meals and Smoked Meats sells reasonably well.
First four Arena fights are relatively easy, if you go in at full stamina and run around to kite opponents to take them one at a time (fifth fight will be a boss of sorts).
You can use hirelings to do fightig for you, Dog + Jones works pretty well, are cheap to hire, and will "respawn" back at the inn when they die. You just need to talk to the dog to set it into attack mode at every location. They will clean graveyard, mines, or hunt boars without any help from Lona.