OU will only be used when
- AD server is organized with specific structure
- want to add thin client into speicific node after joinning the domain
You can leave it as empty so that by default every of your domain joined thin client will be in the node of "Computer".
If you want to put the TC in a specific OU, you must input the full LDAP path of the organizational unit. The full LDAP path name is a null-terminated string that contains the RFC 1779 format name of the organizational unit (OU). For example, ou=OU1,ou=OU2,DC=DMServer,DC=com
You have to convert the special characters on your own if there is any.
For example, if the OU name is #\/, , when you input its full LDAP path, you need to convert them as below.
ou=\#\\/\,\ ,DC=DMServer,DC=com
Hope the explanation helps.