There are several Inversion of Control (IoC) containers for .NET to pick from (such as Castle Windsor, Structure Map and Microsoft Unity, just to name just a few). Ninject is one of the newest entries in the arena.
Here is the program that we would be using to demo NInject.
Unity is a library like many others that allows you to get an instance of a requested type without having to create it yourself.
As a developer, all we care about is programming language, patterns, UI & data storage. However users do not care how the hell it is implemented, all they care is that does it useful or solves the given problem.
There is no point in blaming each other, we have to understand the each other to be successful.
Dependency Injection allows us to inject objects into a class, instead of constructing them internally. Unity is a dependency injection container that we can use for constructor, property, and method call injections.
You can get good idea about dependency injection by reading this post.
In this article, you can learn how to use Unity with WebAPI.