[Note: due to bugs in the game, it’s advised to follow the sequence mentioned here. If not, it might be that you’re unable to reach the Yeti with the needed items.]
You’re standing in front of your house. Go inside and look around. When you look at your plate, you realize you’re not hungry but you take the FISH.
Go to the left and go inside the house of the professor. Talk to him and ask at least about the monster. He’ll tell you it’s a Yeti. You can ask about the red cup, watch some TV (there’s only snow on it) and watch some books but these are only interesting for your parents. Give him the fish and you’ll get a MAP in return. Leave the house.
Go to the right and enter your own house again. Look at your plate to get another FISH. Look at the picture on the cabinet. It’s you when you were little. Use the bottom drawer and take the KNIFE out. Talk to your dad and ask about the monster. He can tell you little and refers you to your mother. Also ask for your pocketmoney. You won’t get it. Talk to your mum and ask about the monster again. Leave the house.
Walk twice to the right and find some big feet in the snow. Walk right again to see the house of your uncle. Go inside and find him…. dead. Try to talk to him but he won’t answer. Look at that hole in the wall!. Open the drawer to take a STICK out. Then leave the house again. You have to tell your parents!
Walk to the left twice and enter the house. Talk to dad. The monster has to be defeated. You promise you won’t go unarmed. You already go your knife. Use the knife on the stick to make it sharp. Now you have a spear as well.
Leave the house and go to the left twice. Meet the Yeti.
Now there are two ways to get rid of the monster, the violent way and the peacefull way.
The violent way:
Use the spear on the Yeti. You’ll hit his heart and he’ll die.
The peacefull way:
Talk to the Yeti and learn that he’s lost. Give him the map.
Game source: A copy of the game was found here on the internet.