a.k.a. SIP trunk, voice gateway, connects to the VoIP provider, ITSP [Internet Telephony Service Provider]
Setup provider proxy address and user account information. The labels on the gateways tab correspond with the XML tags on the FreeSWITCH wiki. User Name is often called Peer Name in the Voip Provider UI.
See Caller ID notes in extensions. Also be aware that some providers need you to set "Caller ID in from: true" - this is a setting found under Show Advanced in the Gateways settings.
Effective Caller ID Name, Effective Caller ID Number, Outbound Caller ID Name, Outbound Caller ID Number DO NOT affect the gateway configuration itself, however they ARE used if you enter a dialplan expression to let FusionPBX create outbound dialplan entries for you. So don't try changing these values and expecting any change to the gateway configuration as there isn't one!