hi there i have lost my iphone and i want to find it but i dont know how?

Provided you have Find My iPhone configured before you lost it and the iPhone has Internet connection,

to locate use you computer browser with this link: https://www.icloud.com/#find

If you cannot track it, report to the police, insurance, carrier and change all your passowrds that were used in iPhone.

Lost or Stolen

http://support.apple.com/kb/HT2526