Question: If you want to stain and varnish indoor wood furniture during the winter, how do you do it?

It's below freezing outdoors, but I don't want fumes to accumulate in the house.

Answer: 
I usually stain or apply brushed or rolled on finishes inside. Spray finishes I do in the garage, but quickly, then I immediately bring things inside to dry in an isolated room (usually the master bedroom, which has an attached bathroom.) I leave the fan on in the bathroom, which pulls the fumes out. If you're spraying from rattlecans or a gun, it's important to keep the materials inside until you're ready to spray, or they'll go on strangely because they're cold and sluggish. Your compressor needs to be outside though or you'll get serious amounts of condensation in the air lines.
I have a huge problem with paint and stain fumes. I love these projects but the fumes really get to me. 

Today I found a good solution. I am very proud. Like said above, put the done woods in a closed room and close off the heater vent in that room. Use a fan and open a window. What I did was add a fragrance oil burning kit. The room will smell pleasant. 

Note: always wear protective glasses and mask when painting + staining. You will be less dizzy than me when you are done.