ModRefiner-about reference structure

I am currently working on GPCR homology modeling and I'm new to it.I use ModRefiner for minimization on the structure,but I do not have a reference structure.So,I want to ask:1.What is reference structure?Does it refer to my model sequence in fasta or a second structure? 2.Can I still use ModRefiner for minimization on the structure without a reference structure.If the answer is YES,will it affect my outcome?
Look forward to your helpful reply.Thank you.