Yeah, I agree, a tutorial is much needed, would've done but I didn't have enough time ! When going to the house tile you empty the fishes in your inventory, after a certain amount you pass to the next "level", which is harder
You move to the house tile (if it's in the right you move to the right and you hear a sound effect) and you see in the upper left that your inventory has been emptied and that you made progress. You don't enter the house really, but you see that it did something if you have fish in your inventory. In the upper right you see the "level" you're in.