Wi-Fi is primarily a local area networking (LAN) technology designed to provide in-building broadband coverage. It is based on IEEE 802.11 specification.
This tutorial gives you basic understanding on Wi-Fi.
This reference has been prepared for users to help them understand the concepts related to Wi-Fi
Before you start proceeding with this tutorial, I'm making an assumption that you are already aware about basic telecom concepts like LAN, Duplex, ISPs etc.