After you download the installer for the Discovery Probe under Admin -> Discovery -> Probe, you will be taken through the first time configuration wizard. After entering the Domain Name/IP Address and credentials for your AD, the Probe will fetch your OU structure and you can select which OUs for which you want to sync the users to Freshservice.
You can also enable a custom mapping from your LDAP fields into the Freshservice user fields. Here is the default mapping:
AD Fields
Requestor Fields
First Name
First Name
Last Name
Last Name
Email
Email
Phone
Phone (Work)
Mobile
Phone (Mobile)
Manager
Reporting Manager
Title
Title
Department
Department
Street + P.O.Box + City + State/Province +Zip/Postal Code + Country/Region
Address
To define a custom mapping, please follow the steps in this document:
https://support.freshservice.com/support/solutions/articles/221819