Usage:
ps [options]

Basic options:
-A, -e all processes
-a all with tty, except session leaders
a all with tty, including other users
-d all except session leaders
-N, --deselect negate selection
r only running processes
T all processes on this terminal
x processes without controlling ttys

Selection by list:
-C <command> command name
-G, --Group <gid> real group id or name
-g, --group <group> session or effective group name
-p, --pid <pid> process id
--ppid <pid> select by parent process id
-s, --sid <session> session id
-t, t, --tty <tty> terminal
-u, U, --user <uid> effective user id or name
-U, --User <uid> real user id or name

selection <arguments> take either:
comma-separated list e.g. '-u root,nobody' or
blank-separated list e.g. '-p 123 4567'

Output formats:
-F extra full
-f full-format, including command lines
f, --forest ascii art process tree
-H show process hierarchy
-j jobs format
j BSD job control format
-l long format
l BSD long format
-M, Z add security data (for SELinux)
-O <format> preloaded with default columns
O <format> as -O, with BSD personality
-o, o, --format <format>
user defined format
s signal format
u user-oriented format
v virtual memory format
X register format
-y do not show flags, show rrs vs. addr (used with -l)
--context display security context (for SELinux)
--headers repeat header lines, one per page
--no-headers do not print header at all
--cols, --columns, --width <num>
set screen width
--rows, --lines <num>
set screen height

Show threads:
H as if they where processes
-L possibly with LWP and NLWP columns
-m, m after processes
-T possibly with SPID column

Miscellaneous options:
-c show scheduling class with -l option
c show true command name
e show the environment after command
k, --sort specify sort order as: [+|-]key[,[+|-]key[,...]]
L list format specifiers
n display numeric uid and wchan
S, --cumulative include some dead child process data
-y do not show flags, show rss (only with -l)
-V, V, --version display version information and exit
-w, w unlimited output width

--help <simple|list|output|threads|misc|all>
display help and exit

For more details see ps(1).