For complete PyMol help, click here.
The following is a condensation prepared by Craig Martin (2007).

Selection in PyMol

Select selectname, expression

Expressions - direct

To identify explicitly:
/object-name/segi-identifier/chain-identifier/resi-identifier/name-identifier

commonly:

///chain-identifier/resi-identifier/name-identifier
Examples:
///A/125/CA
///D/58/NZ

Expressions - indirect

Single Word
Selector
Short
Form
Description
all*All atoms currently loaded into PyMOL
nonenoneNo atoms (empty selection)
hydroh.All hydrogen atoms currently loaded into PyMOL
hetatmhetAll atoms loaded from Protein Data Bank HETATM records
visiblev.All atoms in enabled objects with at least one visible representation
presentpr.All atoms with defined coordinates in the current state
(used in creating movies)

Matching
Property
Selector
Short
Form
Description Identifier - List of Example
symbol e. atomic symbols 1- or 2-letter chemical symbols from the periodic table select PolarFe, symbol o+n+Fe
name n. PDB Atom Names up to 4-letter codes for atoms in proteins or nucleic acids select carbons, name ca+cb+cg+cd
resn r. Residue Names 3-letter codes for amino acids select aas, resn asp+glu+asn+gln orup to 2-letter codes for nucleic acids
select bases, resn a+g
resi i. Residue number up to 4-digit residue numbers select mults10, resi 1+10+100+1000
select nterm, resi 1-10
chain c. PDB Chain ID single letters or sometimes numbers select firstch, chain a
segi s. Segment ID up to 4 letter identifiers select ligand, segi lig
ss ss secondary structure single letters select allstrs, ss h+s+l+""

Other property selectors - select by comparison to numeric identifiers:

Numeric
Selector
Short
Form
DescriptionArgument Example
b b b-factor-value real number select fuzzy, b > 10
q q occupancy-value real number select lowcharges, q <0.50
  formal_charge   fc. formal charge-value integer select doubles, fc. = -1
  partial_charge   pc. partial charge-value real number select hicharges, pc. > 1

Useful commands
hide representation
show representation
e.g. hide sticks, show cartoon, etc
zoom selection-expression zooms display to focus on selection
color specific-color, selection-expression e.g. color red, mysubunit2
png file-name save current view as a PNG graphic