A mobile user can connect to a LAN by using a wireless connection which is known as Wireless LAN (WLAN). WLAN uses high frequency waves instead of wire to communicate between nodes. Here signals are of limited range. WLANs combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs. IEEE 802.11 standard provides technical specifications for the wireless interfaces. There are two modes of operations in WLAN.One is the presence of control module often called as based station or IEEE 802.11 calls them access points and the second one is ad hoc or peer-to-peer connectivity. Three basic medium access control (MAC) mechanisms have been defined for IEEE 802.11: the mandatory basic method based on a version of carrier sense multiple access with collision avoidance (CSMA/CA), an optional method avoiding the hidden terminal problem and the third one is a contention-free polling method. The mandatory MAC mechanism and the optional method of IEEE 802.11 are known as distributed coordination function (DCF) whereas the third method is called as point coordination function (PCF). DCF is CSMA/CA with binary exponential backoff algorithm. DCF with optional RTS/CTS scheme in 802.11 MAC protocol avoids the problem of hidden terminals. In this paper, we have studied the 802.11 wireless LAN (WLAN) and the working of DCF in wireless LANs (WLANs).