A direct-sequence transmission — synchronisation, a start delimiter, a header, then the data.
Reading a capture
The header is sent at 1 Mb/s no matter what rate the data uses, so a 54 Mb/s-era network carrying one 802.11b station pays 192 microseconds every time that station transmits. That is the arithmetic behind every "disable low rates" recommendation ever written.
Subfields
SYNC — 128 scrambled one bits, giving the receiver time to acquire the signal and settle its gain and timing.
SFD — Start frame delimiter — a fixed 16-bit pattern marking the end of synchronisation and the start of the header.
SIGNAL — The data rate for the PSDU, in units of 100 kb/s.
SERVICE — Modulation and clock-locking flags, plus a length extension bit.
LENGTH — The time the PSDU will take, in microseconds — not its size in octets.
CRC — A 16-bit check over the SIGNAL, SERVICE and LENGTH fields.