What is the 4th State of Matter and its explanation?What are examples of this?

The fourth state of matter is often said to be plasma.

You can read further details of it here: Plasma (physics) - Wikipedia, the free encyclopedia

This is basically a very hot ionised gas. You can make it in your microwave quite easily with a grape, but it may well damage the microwave.

Here is a website detailing the technique:
Microwave Grape Plasma

This state of matter can be seen in the form of lightning. Ball lightning is a longer lasting version (or at least this is the most favoured explanation). The Wikipedia page above details other examples.

If you have further questions, feel free to ask:)