I am currently going through a car tutorial and was wondering if someone could help.

When i went to convert my polys to sub ds to see how I was progressing, it came up with the message

Error: polyToSubdiv1 (Poly To Subdiv Node): One or more edges is nonmanifold.
// Nonmanifold geometry cannot be converted to a subdivision surface.
// To clean up nonmanifold edges, use Mesh->Cleanup with the nonmanifold option. //
// Error: Command polyToSubdiv failed. Open Script Editor for details. //

When I went to clean up it all turned to faces option,What does it mean clean up nonmanifold edges.???

Jason