PyMOL is governed by a series of concepts that you should eventually become quite familiar with if you are to get the most out of the program.
Unique Names | Objects | Name Patterns | Selection Expressions
Frame | State
Atom | Bond | Residue | Chain | Segment
Fragment | Molecule | Molecular Object
Alternate Locations (as identified in PDB files)
Command | Method
Internal GUI | External GUI | External GUI Skin