The GLD has 8 FX units which can operate simultaneously. The can be configured in a mono/stereo send-return configuration (Setup-Config-Mixer config,) or as inserts on individual channels/buses (FX-FX engine-Back Panel.)
By default in the LR template, the (stereo) return channel strips for send-return configured FX engines are on layerC of bank2, but as with anything, you can re-arrange them using Setup>Control>Strip Assign.
In terms of routing, they’re treated like input channels, in that by default they’re routed to LR and assigned to the auxes prefade, but not assigned to the groups. Like input channels, you can un-assign them from LR (select LR, press the routing button, FX return tab) and re-assign them to groups (select group-routing button-FX returns tab, or, select the FX return-routing button-group tab.) You can take them in or out of auxes using the “Mix” buttons, either on the aux master or the fx return, the same as you would input channels. You can also assign them to DCAs the same way you would input channels.
In terms of processing, the FX returns only have a peq. If you want more processing (eg you want to compress the return) you can assign the fx return to a bus and use the bus compressor, and/or you can change a pair of input channels 1-48 to source their input not from physical inputs, as is their default, but from the FX engine outputs, effectivly giving you hpf, gate, peq, comp and delay on those returns.
Play with Editor to get a better idea.
HTH
