how can i battle the ghost and where
Ok here is a complete walkthrough to meet the ghost:
After you have reached level 9 and defeated the boss in the forest, talk to Bert at the guild, and he will inform you that Evie is at the abandoned house. After talking to her, you'll need to figure out a way to stay up late and visit the abandoned house after midnight.
You'll need alchemy to do that. If you don't know alchemy, buy the alchemy book from the alchemy shop. You'll be able to craft energy potions if you craft at least two items. Energy potions need a mushroom from the forest to craft, so get the "treasure finder" from the accessory shop to help you find one. Energy potions will allow you to stay up late and meet the ghost at the abandoned house after midnight.
Talk to Evie the next day, and she will inform you that you'll need a spirit stone to be able to fight the ghost. The spirit stone is sold at a secret shop next to the guild at night.
Equip it, use an energy potion, and visit the abandoned house after midnight to meet the ghost.
Talk to the bartender for any hints on what to do next.