what are Lists?

It is written in somewhere that Lists are better compared to Arrays for ease of use.

Are they as fast? what are they? are they in unity 3? where can i read about Lists?

Lists are typesafe ways of producing a collection that can be modified at run time - increasing or decreasing the size. They are preferable to arrays because of typesafety, they also have a number of useful methods that can really speed things up. A List provides the same array access operator and can be used in place of arrays in many circumstances. Here is the documentation on lists List<T> Class (System.Collections.Generic) | Microsoft Learn

Lists are very fast - adding to a list can cause the need for garbage collection however.

In C# you must add

  using System.Collections.Generic;

To your file and then you define a list like this:

   List<int> myIntList = new List<int>();
   List<MyOwnClass> myClassList = new List<MyOwnClass>();

In Javascript it works like this:

var myOwnClass = new List.<MyOwnClass>();
var myIntList = new List.<int>();

You can add elements using Add or AddRange - remove them using Remove and RemoveAt, access elements using myIntList[1], the number of elements in a list is stored in a Count property rather than Length. You can sort lists etc.