Hey Tomas Ploquin,
Great question. In regards to flipping, the house "appreciates" through the work you have done to the house to make it more appealing to buyers. For example, if a house has old carpet throughout and bright yellow paint in the interior with old brown kitchen cabinets, a flipper will take out the carpet and replace it with nice tile, paint the walls a more appealing color, and repaint or insert new kitchen cabinets. All of this work will add value to the home and therefore make the home "Appreciate".
You can estimate the "appreciation" by looking at other homes that have sold in the area of the home you are looking to flip. Lets say you see a home that is the same square footage and has the same qualities as the house with the old carpet, ugly paint & old cabinets has recently sold for $100,000. Then lets say you see a home that has similar square footage and floor plan but with the updated interior sold for $200,000. You can assume that if you make the original uglier house look more appealing, then the home will "appreciate" $100,000 by the time the renovation is complete.
It gets significantly more complicated than that but this is where most people begin to grasp the basic understanding. When comparing these homes, you will need to make sure the homes are all in the same general area. In many cities in America, the value of two similar homes can be significantly different than the each other because one home is only half a mile away, but in a worse neighborhood. There are many other metrics used by flippers to determine the future value of the home. You and I will learn more as we continue our journey.
Good Luck!