First, get broadband internet subscription ie, DSL, Cable. Second, purchase a wireless router and wireless adapter if your PC doesn't already have them available. That's about it.
When you have broadband internet, you get a modem. The telephone line or cable goes to the back of this modem. From that, you connect an ethernet cable to the WAN port from the back of the modem and goes into the back of your wireless router.
As for the wireless adapters, they plug into your PC by means of PCI slots, integrated, or USB. Once those are hoooked up, you got instant internet.