If you already have a LDAP directory with existing users, you can import them in IDM using a reconciliation. By default, LDAP users who doesn't exists in IDM are not imported, if you want to import them, you need to modify the reconciliation policy.
In the resource tab, select your LDAP Directory (enable the checkbox)
in Resources Actions button, choose Edit Reconciliation Policy
For the UNMATCHED situation options, choose Create new user based on resource account
Save the policy
To proceed the reconciliation:
In the resource tab, select your LDAP Directory (enable the checkbox)
in Resources Actions button, choose Full reconcile now
You can check the reconiliation status using Examine Account Index subtab.