Every country has their own rules regarding the regular inspection of safety and emissions in vehicles. Some take it more seriously than others, depending on population size, number of cars, and the amount of air pollution in each country.
The emissions are the amount of pollutants that leave the exhaust. This is the waste created by the burning of the fuel in the engine. In a brand new car, the exhaust is usually minimal. But as a car ages, it becomes less efficient and increasingly dirty in its emissions.
If an engine is burning up oil due to damage, it can greatly add to the emissions coming from the exhaust. Countries have regulations for these because with millions upon millions of cars in one country, that makes for a tremendous amount of pollution.
An example of an international difference between emissions standards is the old version of the Volkswagen Beetle. The older version, even when new, creates too much pollution from its exhaust for the United States standards. So, the U.S. ended production of that older version some time ago. However, Mexico did not share the same standards. So, VW manufactured them out there instead.
Vehicle safety inspection helps protect individuals from dangerous situations like a cracked windshield or brakes that are wearing too thin. Sometimes safety inspections are only required every other year.
In many states, registration cannot be completed until the emissions and safety inspections have both been passed. The owner of the vehicle gets a form from the auto center reporting the vehicle has passed. Then the owner must bring this to the Department of Motor Vehicles to register.
Each state has different laws and regulations for this process, and some do not even have to do inspections. But in Utah, emissions and inspections are something every vehicle owner must comply with, in order to maintain the right to drive a vehicle.