Having an unlocked phone allows you to do great things like switch carriers and sell your phone online. If you’re unsure if your phone is unlocked, the most obvious first step is to call your carrier. They should be able to tell you straight away.
Barring that, another thing you can do is try inserting a SIM card from another carrier. Obviously, this method requires a friend or relative with a phone from another carrier. You’ll need to 1) remove the SIM cards, and 2) insert the SIM card from the other device into yours, first ensuring that it is the right size.
Typically, the device network name will change in the upper left or right hand corner of your smartphone if the device is unlocked. If there is no clear indication as to whether the phone is unlocked, you might try turning the device off and then back on. Sometimes rebooting can help recognize another SIM/Network.
If you determine that your phone is not unlocked, learn more about how to unlock the phone by reading on.