problems converting poly's to subdivs
 

hey everyone whenever i try to convert polygons to subdivs i get an error that says to look in the script editor for further information, so i do that and the script editor tells me that one or more of my vertices are non manifold and that i should use the clean up command with the nonmanifold option turned on, so i get into the clean up options and set the nonmanifold, problem is i dont know what i'm doing in clean up (i dont even know what cleanup does) and also i dont know what nonmanifolds are, any explanation of what all this means and how to work it would be great. thanks in advance everyone

There's a few ways to create non-manifold geometry, three or more faces sharing an edge, two or more faces share a single vertex but no edge and adjacent faces have opposite normals. It's all in the manual.