CSharp: Dates in universal sortable format

Question:

How to format dates as sortable universal standard format strings in C#?

CSharp: Pad Numbers with Leading Zeros

Question:

How to pad a number with leading Zeros?
How to get a 8 digits number block, where empty places are filled with zeros?
Formating a number with leading zeros.

CSharp: Implement Indexer

Question:

How to implement an indexed property in c# ??
Do you have an example implementation of an Indexer in c#?