in a forest, I am going to install Exchange 2010 and 2013, coexistence environment.
After researching, I need to first install Exchange 2010, and then install 2013. right?
Pls give me some instructions about the process, related blogs or articles are appreciated

Here some informative resources that might helps you to get in more details and lets you to accomplish this task.

Steps to install Exchange 2013 in Exchange 2010 environment: http://exchangequery.com/2014/02/13/steps-to-install-exchange-2013-in-exchange-2010-environment/

Exchange 2010/2013 Co-Existence Experience: http://www.bctechnet.com/exchange-20102013-co-existence-experience/

Exchange 2010/2007 to 2013 Migration and Co-existence Guide: http://msexchangeguru.com/2013/05/10/exchange2013-migration/

Off-topic, while need to move mailboxes between exchange servers, you may try this automated solution which lets you to get real-time coexistence between two Exchange Servers during the migration period.

Hope it helps you!

Thanks. Very helpful.

I get this error when installing Exchange 2010:

Summary: 5 item(s). 2 succeeded, 3 failed.
Elapsed time: 00:00:50

Configuring Prerequisites
Completed

Elapsed Time: 00:00:14

Languages Prerequisites
Completed

Elapsed Time: 00:00:13

Hub Transport Role Prerequisites
Failed

Error:
Setup encountered a problem while validating the state of Active Directory: Active Directory error 0x800705B4 occurred while searching for domain controllers in domain forestB.local: This operation returned because the timeout period expired.
.
Click here for help... http://technet.microsoft.com/en-US/library/ms.exch.err.default(EXCHG.141).aspx?v=14.3.123.3&e=ms.exch.err.Ex28883C&l=0&cl=cp

Elapsed Time: 00:00:06

Client Access Role Prerequisites
Failed

Error:
Setup encountered a problem while validating the state of Active Directory: Active Directory error 0x800705B4 occurred while searching for domain controllers in domain forestB.local: This operation returned because the timeout period expired.
.
Click here for help... http://technet.microsoft.com/en-US/library/ms.exch.err.default(EXCHG.141).aspx?v=14.3.123.3&e=ms.exch.err.Ex28883C&l=0&cl=cp

Elapsed Time: 00:00:06

Mailbox Role Prerequisites
Failed

Error:
Setup encountered a problem while validating the state of Active Directory: Active Directory error 0x800705B4 occurred while searching for domain controllers in domain forestB.local: This operation returned because the timeout period expired.
.
Click here for help... http://technet.microsoft.com/en-US/library/ms.exch.err.default(EXCHG.141).aspx?v=14.3.123.3&e=ms.exch.err.Ex28883C&l=0&cl=cp

Elapsed Time: 00:00:09

can you help pleaseMany thanks

Exchange installation error for Hub Transport Role Prerequisites: https://social.msdn.microsoft.com/Forums/exchange/en-US/8771bede-025c-4b91-a51b-ec3751283a18/exchange-installation-error-for-hub-transport-role-prerequisites-client-access-role-prerequisites?forum=exchangesvrdevelopment

Exchange 2010 Installation in 3 STEPS: https://telnet25.wordpress.com/2010/06/14/exchange-2010-installation-in-3-steps/

Also, check this which lets you how to Install Exchange 2010 in Step by Step: http://blogs.technet.com/b/ferris/archive/2010/03/05/howto-install-exchange-2010-step-by-step.aspx

You may also take help from the below given earlier discussed threads:

Exchange 2010 HUB/CAS node installation error: https://social.technet.microsoft.com/Forums/en-US/1028eb39-40ed-4810-8da9-9ffa1faa055f/exchange-2010-hubcas-node-installation-error?forum=exchangesvrdeploylegacy

https://social.technet.microsoft.com/Forums/en-US/b83ba6de-7d51-4594-a439-2f12fa4e5618/installation-of-exchange-2010-sp1?forum=exchange2010