How to use laptop as a WIFI hotspot ?

For this you'll need -

Virtual Router 

http://virtualrouter.codeplex.com/

Steps -
1. Download virtual router.
2. install it.
3. open Virtual router , choose shared connection and enter password.
4. Start virtual router.

To use it in your mobile -
Goto Menu > Wireless and netorks > WIFI settings > enable WIFI and wait for few seconds .
You'll get Virtual router notification in WIFI networks , press on it and enter the same password of virtual router and connect it .