Presuming this is a delay/thickener'/speader of some sort. The placment is fairly variable. You might want to put the track prep' stuff like eq, or comp up front. The thing's apt to have a 'stereo out option (spreading?
'Delay as well as the doubler'?
As often it's best just to try this stuff out and gather your fave sound results from there.
For vocals, I will tend to use it as an aux send. But I will send the output of the aux send to the group buss that the vocals are sent to, and that group buss has the overall EQ and compression used for all the vocals. (individual vocal tracks may or may not have EQ and compression on them individually)