AI stands for artificial intelligence, where intelligence is defined as the ability to acquire and apply knowledge. Artificial Intelligence is a branch of computer science that aims to create intelligent machines. It has become an essential part of the technology industry.
Research associated with artificial intelligence is highly technical and specialized. The core problems of artificial intelligence include programming computers for certain traits such as:

Knowledge engineering is a core part of AI research. Machines can often act and react like humans only if they have abundant information relating to the world. Artificial intelligence must have access to objects, categories, properties and relations between all of them to implement knowledge engineering. Initiating common sense, reasoning and problem-solving power in machines is a difficult and tedious approach.
Machine learning is another core part of AI. Learning without any kind of supervision requires an ability to identify patterns in streams of inputs, whereas learning with adequate supervision involves classification and numerical regressions. Classification determines the category an object belongs to and regression deals with obtaining a set of numerical input or output examples, thereby discovering functions enabling the generation of suitable outputs from respective inputs. Mathematical analysis of machine learning algorithms and their performance is a well-defined branch of theoretical computer science often referred to as computational learning theory.
Machine perception deals with the capability to use sensory inputs to deduce the different aspects of the world, while computer vision is the power to analyse visual inputs with a few sub-problems such as facial, object and gesture recognition.
Robotics is also a major field related to AI. Robots require intelligence to handle tasks such as object manipulation and navigation, along with sub-problems of localization, motion planning and mapping.

Why We Need AI
We are growing at huge rate, say it in terms of population, scripted knowledge, tasks etc. Increasing in scale also increase entropy in system, demanding huge number of tasks to be automated, and centralized. AI in simple words is implementing human senses in machines. Humans will surely benefit from AI. Though we are seeing automation of tasks is leading to job cutting, in long term it is going to turn out to be a major benefit.
AI can surely process all trivial tasks at huge pace compared to humans.
Traffic Control, Automating Support, Automating Manufacturing, Fraud Detection, Imposing Laws without corruption etc. It has many good uses.