LAN (Local Area Network) is easy to connect to. The majority of home and business LANs now support wireless meaning you can connect to it with a wireless device.
If you have a device that supports Wi-Fi then look for the option to enable it, on a Windows OS it is normally a set of bars in the bottom right corner. Once you have it open you can then select the network, you may be asked for a password. If you have the password and you're allowed on the network then you shall be connected to the LAN.
A second option would be to plug a Cat5, Cat5e or Cat6 (ethernet cables) into an ethernet port on your computer and the other end into either the modem/router directly or into a network switch/socket (normally used in larger buildings or when you have many wired connections).