vCenter server appliance (VCSA) is a management software by which you can manage ESXi host and VMs.
How To Join VCSA to Windows Active Directory:
1. Launch and log in to VCSA using vSphere Web Client.
2. Open home>go to Administration > Deployment > System Configuration.
3. Click on Nodes and select the required node.
4. Navigate to Manage > Settings > Advanced > Active Directory and click Join.
5. Put the required details.
Put Active Directory Domain Name.
Put the OU name for the VCSA (optional).
Put the user with Domain joining rights/administrator.
Put the password of above user.
6. Click OK, and restart the appliance.