CDMA stands for Code Division Multiple Access. It is a channel access method. It employs spread spectrum technology (Direct Spread Spectrum).
Transmitter Side:
In CDMA, a narrowband message signal is multiplied by a very large bandwidth signal celled the spreading signal. This spreading signal is a Psuedo Noise Code signal. All users in CDMA system use the same carrier frequency and may transmit simultaneously. Each user is identified by it's own psuedorandom codeword. This psuedorandom codeword is orthogonal to one another. In this way, each user is separated from the others.

Receiver Side:
For detecting the message signal, the receiver needs to know the codeword used by the transmitter.