When I'm adding subdivision modifier my object freaks out. I'm new to blender and don understand why :o if somebody knows why, it would be greatly appreciated.
here is without

When I'm adding subdivision modifier my object freaks out. I'm new to blender and don understand why :o if somebody knows why, it would be greatly appreciated.
here is without

In the picture below, you can see the effect of extra edges placed where you need a surface to keep its shape, that is, have sharper corners or edges. The bottom row has a smoothing modifier on it. So you have to cut more edges (or use Loop Cut as edna said), where you need an edge or corner to be sharper.
The modifier is doing what it is supposed to. So the answer depends on what you were expecting. Experiment with one or all of these to get the result you are after: