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IF the 'meter/main' is the first means of disconnect, the neutral has to be tied into the ground at that point. A insulated neutral, bare or insulated ground, and your phase conductors (hots) go from the "main" to the sub-panel.
At the sub-panel, the neutral terminal block has to be insulated from the enclosure, hence the plastic insulation. The ground bar has to be mechanically 'bonded' to the panel enclosure. This is usually accomplished via a bond screw into a tapped hole, a bond strap, or any other suitable means.
The mfg instructions provide a list of approved 'parts' that may have to be purchased separatley to provide a SAFE and code compliant installation.
From your wording, you need to purchase a CH ground bar at the supply house. The insulated 'neutral' bars are for neutral conductors only within a sub-panel.