after installing a domain controller how a computer is connected to server

Assuming all the network settings, IP addresses, gateways etc are OK.
On the client you wish to join to the domain:

Right click "My Computer", select "Properties".
On the "Computer Name" tab, click the "Change" button.
In the "Member of" box, click the "Domain" button, and enter the domain name.
Click OK.

Hi Jasom,

Great, before joining the PC, get these handy.

From DC
1. DNS IP Address
2. Domain Name (ex: sitename.org)
3. DC name (assuming it is dcname)
4. Username and password for a Domain Admin

On PC:
1. Check wether the PC has the proper IP address
2. Make sure of DNS IP
3. See if Gateway is required
4. Start -> Run -> Cmd -> Ping IP Address of DC [Working?]
5. Also ping dcname.sitename.org {Working?]

Joining Steps:

Right Click on My Computer --> Properties --> Computer Name -> Change -> Click on Domain Name and give you Domain Name (sitename.org)
Click OK, when prompted for Usernam & Password, give them
Ok OK, Reboot
You are done on DC, you can open start -> run -> dsa.msc and under the Computers OU, you can see the Machine Account

Here are couple of links to do the same....

http://www.petri.co.il/joining_a_domain_in_windows_xp_pro.htm
http://www.windowsnetworking.com/articles_tutorials/wxpjoind.html

Thanks
Nitin Gupta (gupnit)
http://www.nitingupta.in