This web site really helped me out when I was trying to understand lab values. It is a really great tool and I believe a little easier than some text books Lab Tests Online: Welcome!
The RDW is Red blood cell distribution width--it is detecting the size variation in red blood cells.
If you are referring to lymphocytes--they produce antibodies--they are a type of B-cell.
The SEG is a type of neutrophil-a type white blood cell
Check out these URLs as well:
Low White Blood Counts (Neutropenia): Cancer Center: UI Health Topics
WBC Differential: The Test
Medscape: Medscape Access
Hope these help
and Good luck in your studies!!!