Well here we go .......

1) Your local "after-market" auto parts store (AutoZone, O'Reiley's, PepBoys, etc) usually stock a Chilton Manual for your car ... but I'm sure you already have one.

2) Section 3-17 has a couple of pictures, depicting the hoses and couplings just like your pictures (only yours are better)

3) To disconnect the heater hoses from the heater housing inlet and outlet pipes at the firewall, see illustration. NOTE: The coolant hoses are equipped with special locking couplers at the heater housing on the firewall. Press the tab on the coupling (tab is at the firewall end of the fitting) and pull the hose to disconnect it from the coupling device on the heater housing.

They do have a couple of arrows on their pictures, pointing out the tab referenced in the instructions -- hope this helps

Hopefully the supplier you reference is a GM dealership ........