Travelling to Newark, New Jersey

Matthew, please add a "location" to your profile, so answers can be customized for you.
I go to Newark two or three times a year, usually to the Newark ( .. art) Museum. I have to assume you have a family reason for going there, since it is a poor location to "visit New York City" on a daily basis from. But it can be done, if you insist.
Newark is an aging, post-industrial city, with a lot of budget and social problems. I don't like to call any city unsafe, especially since that is erroniously said often about New York City. But unlike NYC, Newark had to recently lay off 30% of their police department to save money.
Newark has excellent train transportation from the airport to Newark Penn Station. That is nominally "downtown", but actually near the Passaic River, not a residential area. Newark has a subway/streetcar system which covers some, but not all parts of the city. I am sure that free street parking is difficult, time-consuming, and annoying, just like in other big cities, so you would only want a car to visit suburban New Jersey, and so on.
Your OP is very low on details that might help get a better answer. You need to describe your trip's purposes, your budget, and your travel needs.

Firstly, thanks for the detailed information, I am from Topeka, Kansas. My friends are insisting to visit Newark (Prudential Center) as they are basketball fans. As we get off for one week, we will visit New York for sightseeing after visiting Newark. Budget is not an issue, but as you said about police and crimes, i have to consider our safety. We just want to have a wonderful trip with great food and adventures.

Listen, Matthew, I consider myself a good reader of internet "affect". But " As my friends booked a car from a website." sounds like English as a Second Language to me. If you are travelling in March and want to see College Basketball, you wouldn't go to Newark. Look up the NCAA schedule. Newark has some history for Italian food (fading today ... ) and Portuguese food in the river (Ironbound) area. But the motels budget travelers use in Newark don't even have sidewalk access to mass transit to NYC. I suggest you stay in NYC instead. Use the internet to check the Barclays Center and Madison Square Garden athletic schedules. Newark (EWR) is a good airport, with respectable transportation to NYC. That does not mean that Newark NJ should be your "destination". You need to measure cost against convenience. Also see TripAdvisor messages about staying outside NYC for visiting NYC. The advice is always, stay in NY if you can afford it. Even the cheaper Long Island City (a part of NY City, not another place) has subway (mass transit) access to everywhere in NYC.

Thank You TIM for your valuable guidance. This helps me alot. I will tell about this to my friends and surely stay in NYC. Thanks alot for the tripadvisor website. I checked this website. It is very useful about taking decision based on where to stay and which place is best for food.

You're not going to see any type of basketball at the Prudential Center be it the NBA or NCAA, plenty of NHL hockey though!

To address the transportation aspect of your question, airport websites are usually good sources of information. For Newark, look at http://www.panynj.gov/airports/ewr-public-transportation.html and its transportation section. As you will see, much of the orientation is towards New York City, because that's where many travellers are headed. But if you want to see Newark, go right ahead with the information you will find on the link.