A LAN card connects a computer to a network, whether local or foreign. LAN cards typically connect to a computer's motherboard via a serial port. There are other varieties that connect via a SATA, eSATA or USB port.
Almost all LAN cards that are released today have wireless radio capabilities built into them. These are known as WLAN modules. They allow a computer to connect to a network not only through an RJ-45 Ethernet cable but also via 802.11 wireless network signals. The speed capabilities of each LAN vary by its own specifications. Some LAN cards are able to do 10/100 mbps, while others are rated 10/100/1000, meaning that they are able to access up to a one gigabit network speed.