Dial the trunk or trunks assigned for remote access, the trunk will answer with stutter dialtone, dial an assigned barrier code and you will recieve system dialtone, at this point, they are acting as a part of the system and can dial any extension or dial '9' to make a call using the systems trunks.
If you are going to allow users to dial '9', you will probably need to change the ARS FRL for barrier codes from 0 to 3 or higher or a restriction level of 'Toll' (recommended) or 'None'.
You can track remote access call but the SMDR must be programmed to track incoming calls.