Like a movie critic's job is to watch movies and tell everyone what they thought of the film, a food critic's job is to eat out at restaurants and share his or her opinions on the meal. In addition to talking about the food, most restaurant critics will also critique the service (is it fast or slow, friendly or sullen), the decor, and the price of the dishes. Their goal is to approximate the dining experience so you can see whether you would like it.
The trouble is that not everyone has the same palate. One person may love spicy food while another prefers sweet tastes. Some people like fish, others hate it. So it can be difficult to judge whether your family will like a place based on a one time opinion of an unfamiliar critic. To properly use a restaurant critic, you should go back over their reviews and find out whether they agreed with you on restaurants you have already been to.
Because the opinions of food critics are published in national newspapers and magazines, being reviewed can be a huge boon for a restaurant, especially if they're new and not yet well known. After a positive review, people will rush in to partake of the food. To get an accurate impression of a place, food critics often do not announce their presence in the restaurant so that they are served the same way as you would be if you went into the same restaurant.
In the past, food critics were paid professionals employed by newspapers and magazines, but in the age of the internet anyone can be a food critic, even if their real job is mowing lawns or designing rocketships. Nearly just as important as a food critic review is the opinion of a customer. Patrons often frequent popular online review sites such as Yelp.com and mobile apps like Urban Spoon. Restaurants, retailers, hotels, hair salons, and even dog kennel business' (website) rely on positive customer reviews to help their business.