what is the reason that I need emissions on my car this year but did not need one last year and what do you require to have the testing done?

Jason Winford's answer is correct, but not complete. Some (not brand new) cars are issued a 2 year emissions cerificate, some are issued only a 1 year certificate (depends on vehicle type/age/and emission test values). Additionally, if you happen to drive past one of the "mobile emissions testing" devices, you can receive a roadside "emissions test passed". This is stored in the state system, and linked to your license plate number. If you pass this way, your renewal card that comes in the mail will say so. All that is required for test is to have your car warmed up, take your car to the testing center, have it tested, and pay the fee.

Newer cars are emissions exempt for a period of time before being required to run emissions test. If it's a newer car they usually just scan your system to make sure all your sensors are working correctly. Costs $25 and you get one free re-test if it fails.