Newer red wines will have a bright red or purple color and will change to more of a brick red or brownish with age. White wines change as well, darkening to a deeper gold or losing their greenish or straw color as they age. Before swirling, smell the wine while still to pick up the varietal characteristics. Next, swirl the wine and smell it immediately. You should pick up heavier, more intense smells, which will probably change as the wine settles again.
Smells can be purely subjective, and there are thousands and thousands of options to compare.
They are sensed by taste buds located in different parts of your mouth, hence the need for swirling the wine inside your mouth. To taste the wine, take a sip about the size of a large teaspoonful. Roll it all around your mouth and swallow a little. It sounds complicated, but once you have practiced a few times, you'll be tasting like this without even realizing it. Note how the flavors develop and how they are sustained.