What is cool about generics why use them

Question

What are generics, what are their benefits, why should I use them, where should I use them, and how should I use them?

Keep the answers simple

Answer 1

Okay. For simplification, I am listing it as points:

1. Makes it possible to create type-safe code or use library methods; for example, a list of strings is always guaranteed to be a list.
2. Because generics are utilised, the compiler is able to check the type safety of code at build time, for example, are you thinking to insert an int into that list of strings? This runtime error might be less obvious if you used an ArrayList.
3. It is faster than using objects since it does not require casting from objects to the desired reference  type or boxing/unboxing (where.net must convert value types to reference types or vice versa).
4. It gives you the ability to write code that is applicable to many types with the same underlying behaviour. For example, a Dictionary <string, int> uses the same code type as a Dictionary <DateTime, double>; using generics, the framework team only had to write one piece of code to achieve both results with the benefits.