I had a collapsed lung a week ago. I have a chest tube that is leaking a reddish liquid. What is it and is it normal?

Likely. Sounds like ur home and the leakage is around the tube site? In either case, some leakage is normal. Redness around the catheter site, increasing pain, shortness or breath, fever/chills are not normal and u need to call ur doc.
Chest Tubes. Yes. That is their function. They keep the area pressurized and let any inflammatory fluid, like blood tinged body fluids, drain easily so that other complications do not develop. I would hope that your physician gave you some literature or other instructions on what to watch for.