I have no idea what I'm doing in this game.
The long and short of it is you're trying to figure out what ghost is haunting a house. You do this by finding evidence of that ghost. You can check your journal and record evidence you find in it to isolate which ghost it is.
Talk to the witch at the witch's house to take ghost hunting jobs, and then before midnight head home and go to haunted houses from there.
You have a variety of tools at the bottom of the screen in haunted houses, try to use each one in every room to get the hang of them. If you can't use a tool for any reason, the game will explain why. Check your journal to see what kinds of evidence that you can find, for example: EMF 5 on the EMF reader.
While you're searching for evidence, the ghost is harassing and hunting you. If things get too dangerous, you may need to flee the house before finding all of the evidence, at which point you can just make a guess off of what you've found and hope you get it right.
The areas outside of ghost hunts are where you buy additional tools, take jobs, research ghosts for additional information on them, improve your stats, etc. Additional information can prove invaluable for quickly and safely identifying a ghost.
Things can get more complicated than that as you keep playing, such as ghosts leaving additional evidence to confuse you, harder jobs that only reveal 2 pieces of evidence instead of 3, or ghosts stalking and possessing you. Don't worry about these until you get the hang of the basics though.