What does 2 year contract mean?

I'm planning on buying a iphone 5s, i don't understand the difference if it is in contract or not.

The iphone 5s with contract costs 199$ and the one without costs 649$

If i buy the one with contract does it mean i wll have to pay more mone for the phone?

The contract refers to the phone and the service.

Say you sign a 2 year contract with Sprint for $35/mo for voice and $65/mo for data. Your upfront cost the day you sign the contract is $199 for the phone, and then $100/mo for the next 24 months for your voice & data service.

At the end of your 2 year contract, you may upgrade your phone and enter into a new 2 year contract with Sprint, or go with a new provider or do nothing - keep your iphone 5s and continue to pay Sprint $100/mo for service.

However, if you leave Sprint before your contract has ended, you will hit with the Early Termination Fee (ETF) outlined in the contract (usually several hundred dollars.) So be sure you read and understand the contract before you sign it!

You pay less because it's a discounted price on a contract

http://lmgtfy.com/?q=What+does+2+year+contract+mean%3F

Can I buy it from sprint and just add it on to my existing account?