This KB will show you how to add VMware ESXi Host to VMware VCenter 4.1, this KB also apply to VCenter 5.
Start the VMware VSphere Client, and point to the Vcenter server IP address, Make sure you use the Username and password of the VCenter Server account.
Make sure you create a datacentre first.
After you created your first Datacentre you are ready to go.
Right Click on the Data Centre and click on Add Host
Fill in the Esxi Host Details
Verify details and Click Next
Type License Details If you have or you the Evaluation mode
Enable Lock Down mode if you need (not Recommended)
Check the Task bar to see the progress.