Once vCenter Server is installed, you can go to
http://<Your vCenter server IP address or FQDN name> and click on Download vSphere Client. vSphere Client installation is straightforward. Make sure the user you are working under has local administrator rights on the machine and the system has an Internet connection.
Run vSphere Client by navigating to Start | Programs | VMware | VMware vSphere Client and type vCenter Server's or the host's address; if you are connecting directly to a host, enter the username and password.
You can ignore the security warning that appears. If you are not able to connect, make sure that the VMware VirtualCenter Management Webservices service on the server is running.