I would like to know if my iPhone is unlocked??

Insert a sim card from a carrier that si different to the one you are regularly using.

If you get a "Sim not Supported" error it is not unlocked.

If it works correctly, it is unlocked.

Follow the steps in the link provided above by Limnos, and contact the cellular carrier it is locked to. Only they can authorize the unlock.

How to unlock your iPhone for use with a different carrier - http://support.apple.com/HT201328