Adding

Initailising ArrayLists

The default capacity for a new arraylist is 16 elements.

System.Collections.ArrayList myArrayList; 
myArrayList = new System.Collections.ArrayList(); 

Accessing Elements - Zero Based

Items can be returned using an index that starts at zero.

System.Collections.ArrayList myArrayList; 
myArrayList = new System.Collections.ArrayList(); 
myArrayList.Add("string"); 
myArrayList.Add(20); 
myArrayList.Add(false); 
Console.WriteLine(myArrayList[1]); 

Capacity

You should always try and define an initial capacity for your arraylist if possible.
You can modify the capacity at any time by assigning a value to the Capacity property

myArrayList.Capacity = myArrayList.Count 

Another way to achieve the same result is to use the TrimToSize property

myArrayList.TrimToSize 

When the current capacity is exceeded the ArrayList will automatically double its capacity.

Inserting

Insert - Inserts an element at the specified index.
InsertRange -