If your computer is equipped with wireless capabilities, your computer will have what is called a WLAN module. With today’s advancing technologies, most desktops, laptops, tablets, and cell phones are equipped with WLAN module.
For example, a computer in one room needs to connect with a printer in the next room over. As long as the printer is connected either by a direct connection with an Ethernet cable or wirelessly via a WLAN module connected to the LAN via a router the computer will be able to connect to the printer through the LAN.
LAN cards also make it possible to connect many different computers together through the LAN. As long as each of the computers has the proper IP package addresses.
The speeds of each LAN will vary however. This will be depenanct on the LAN cards themselves. Some are capable of speeds up to 10/100 mbps and then there are some that are rated up to 10/100/1000.
What this means is that some are capable of speeds of to 1 gbps. This all depends on the specifications of the computer when purchased.