The condenser is part of the distillation apparatus. Its top part is connected to the distilling flask and the thermometer by an adaptor and its bottom part leads to the collecting flask. The most common condenser has 2 hollow chambers. In the outer chamber, there is a constant flow of cold water, that cools the glass condenser. The water enters at the bottom part of the condenser and exits at the top part. As the hot vapor enters the inner chamber of the condenser, it's cooled down by the cold surface, condenses, and passes down the condenser into the collecting flask. This setup prevents the hottest vapor from contacting the coldest water, avoiding thermal shock to the glassware.
Figure 1: Process overview of ethanol distillation