In one sentence, describe what the following article is about:

A header is a solid section of wood that is installed over a doorway on a load-bearing wall in order to redistribute the weight and compensate for the studs that were removed to widen the opening to install the doorway. Use a stud finder to see if the space above your door is a solid header.  Look for a solid section of wood that would indicate a header was installed and the wall is load-bearing. If the space above a doorway on the wall is hollow, then it’s likely not a load-bearing wall. Check the beneath the wall to see if it’s stacked on another wall. Go to the first floor, basement, pilings, or crawlspace and look to see if there are piers or girders underneath the wall that would indicate that it is a load-bearing wall. If there is, then it is likely a load-bearing wall.  If the wall you plan to knock down is on the second floor, check to see if there’s a wall in the exact same place on the floor below it. Piers or girders look like solid metal beams and are used to support structures. If you see them below your wall, then it means the wall also supports the weight of the building. If you see pylons, which look like large posts, beneath your wall, it means your wall is load-bearing. Be careful crawling beneath the structure to inspect the walls. If the wall runs through the center of the building and is beneath the trusses or frame of the structure, then it may be a load-bearing wall. Just because the wall runs parallel to the framing above it doesn’t necessarily mean that it’s load-bearing, but it is a sign that it could be and it needs to be confirmed before you try to knock it down. If you see ceiling or floor joists at the edges of the wall, then it’s definitely a load-bearing wall. If you have the original blueprints of the building, there should be a key that includes markings to indicate which walls are load-bearing. Look for an “S” which means “Structural” near walls, joists, and other features on the blueprint. Look for the wall you plan to knock down and determine whether it’s structural or not.  Read the blueprints closely to look for indicators that a wall is load-bearing. Use the key to identify structural features. The best way to determine that a wall isn’t load-bearing is to hire a structural engineer to come out and inspect it. They’ll be able to analyze the structure and confirm whether or not it’s safe for you to knock down the wall.  Look online for structural engineers or engineering firms you can pay to inspect your wall. Hiring a structural engineer can cost between $300-$500.

Summary:
Identify load-bearing walls by solid headers above the doorways. Note that stacked walls are structural and shouldn't be removed. See if the wall runs parallel to the frame for signs that it’s load-bearing. Review the blueprints to confirm if the wall is structural. Have the wall inspected by a structural engineer to be sure.