auto discover process

The Exchange Autodiscover service provides an easy way for your client application to configure itself with minimal user input

Please Read this article
https://msdn.microsoft.com/en-us/library/office/jj900169(v=exchg.150).aspx

i already read this Marcile but its not easy to understand could you please explain in simple words if you can.

ok
in AD environment when user open the Outlook for the First time all information needed to complete added there exchange mail to outlook is just enter there user name and password then all  exchange server details will be setup automatically to there outlook

Try this Experts Exchange answer complete with links.

https://www.experts-exchange.com/questions/27606228/CAS-autodiscover-for-dummies.html

Autodiscover is somewhat complicated because obscure errors can cause it to fail (as I learned at a client).  Review the links in the above answer.

Autodiscover is an IIS virtual directory on the Exchange servers that hold the Client Access Role. This services allows Outlook clients, phone (activesync) to automatically have their phone configured by entering their name and password.

This is useful as users do not have to manually enter settings like mailbox, server etc.

Also there will be a SCP (service connection point) created in on the CAS server role which has the authoritative list of the URL's for Exchange.

Basicically in a netshell Autodiscover is a services that helps clients find their mailbox without having to do any manual confiugration. Take a look at the TechNet below which provides more detail.
https://technet.microsoft.com/en-us/library/bb124251(v=exchg.150).aspx#works

Will.

Hi Will,

you have given 50% answer of my Q but can you please explain me the complete process step by step how it works.

Autodiscover has many parts and methods to determine a connection. The link i have provided below outlines every possible method of Autodiscover and how each process works.
https://msdn.microsoft.com/en-us/library/office/jj900169(v=exchg.150).aspx

Will.