Man pages
Browse the illumos and Solnix command reference — the man pages that ship with packages in the binary cache, grouped by package and section (1 user commands, 2 system calls, … 8 admin). This is the command reference; for concepts and how-tos read the handbook.
Handbook
Read this first — concepts and how-tos.
Man pages
You are here — the command reference, A–Z by package.
Linux & BSD differences
Know Linux or a BSD? How each command differs here.
Package search
Is X packaged, and for which arch?