In some tutorial I noticed that in order to get rid of the wierd lookin (black areas) after pressin smooth button, usin the CTRL L and CTRL N. What do those shortcuts do excatly?
Ctrl+N recalculates the face normals. If you have double vertices or internal faces or non manifold faces this may not be successful so may require your mesh to be better of flip faces manually
Ctrl+L in edit mode selects linked vertices
Before using “CTRL+N” I generally use “A” instead of “Ctrl+L” so that all separate sets get selected.
Also note that there is the option to invert the normals on the left hand toolshelf straight after using “Ctrl+N”.