This page of the Little Nightmares 2 guide contains a walkthrough of the first part of the gameplay: Forest (A Cottage in the Forest). We have described all the interactions you need to perform to get out of the house.
Encounter with Six
Upon entering the house you will find yourself in the kitchen. You can take your time there and engage in activities like pulling things off the table or playing with food in the fridge, but this has no effect on the plot of the game.
Story-wise, you just have to run out of the kitchen and head to the door left ajar on the right wall.
The door leads to the basement. Run down the stairs and look around the area.
You will immediately notice a cleaver that someone has stuck in the chest right next to the stairs. You can try to take it out, but it is beyond your strength.
Move to the wall on the left and you will see Six sitting on the carpet. You need to destroy the wall and get inside.
In order to get to Six, you need a strong tool to destroy the wall first. Head to the right: there is another room that you can easily get into.
You can take the axe out without any problem. All you have to do is jump up to grab it with both hands.
You need to drag the axe to the door blocking your access to Six. This is neither an easy or a pleasant task.
When you reach the door, hit the wall a few times with the axe. This will enable you to move on.
Approach Six. At this point, she will be very insecure and have no desire to see you.
Run upstairs with Six. She will open the door to the dining room. Run inside and continue chasing after the girl.
Your task is to jump on the cabinet (where the shelves are). If you try to climb up the door, you will just fall down.
Jump from the cabinet through the hole in the wall.
Six wants to get out of the house as well. You will join forces and open the entrance to the attic together. Just get close to the girl and she will help you spring up high enough to grab the mechanism which opens the attic.
Don't linger. When a ladder appears, climb up.
Together, push the suitcase so that each of you can climb onto the dresser right next to it. Start this interaction and Six will join to help you push the item.
You need to get the key, but you need to jump further to access it. Again, Six will help you spring up so you can get onto the cabinet.
Use the board located right next to the dresser and slide down safely. Turn left, crouch down and sneak under the cabinet.
You will come across a woman holding a crank that you will need. Grab it and seize it out of her hand.
The crank will fall out along with the woman's arm. Grab it and just go back to Six.
When you place the crank at a specific spot, Six will happily take care of it.
Your task is to climb the cocoon hanging on the right side. Six will turn the crank and lift you higher. Once you're at the top, jump onto the key. You will fall to the floor with it, but you will be fine.
Once you've obtained the key, head to the exit door. When you open them, you'll be able to get out.