It all depends on your phone model. Look for a box that came with your phone. Inside that box is a bunch of things that look like paper with writing on it. If you read that writing, the result is called "instructions" or "manual". In there you will find the secret of WiFi.
please guide me on connecting wifi on my mobile
When you select your wifi function on the phone (on my phone I find the icon on the screen and touch it) it will show you a list of networks within range. If you are in a free wifi zone it should connect automatically. If not you have to select the network you want to connect to and enter the network password. Once you've done this you can cannect automatically to that network the next time you select wifi mode.