Shading issue when adding Subdivision Modifier Firt things first, needless to say that I'm still a newbie haha.

I've been learning how to model with extruding vertex and faces, instead of starting from a cube.

Everything went pretty well until I decided to add a Subdivision Surface modifier to smooth everything and I found this(Also happens when I right click and check shade smooth):



Also I let you see the X-Ray version, which made worry:



So thanks in advance and any help would be appreciated :3
Looks originally like "Normal" problem. this post will give you an idea about it. it happens a lot when models are extruded.

Blender How to Recalculate Normals