There seem to be almost as many different gods and goddesses as there are pagans. In ancient times, different parts of the world worshipped their own gods and goddesses. It is interesting to see the similarities between gods and goddesses of different pantheons.
I personally am eclectic, and I worship and call upon deities from several different pantheons. I began my study of paganism with the Celtic pantheon, and I do most often work with it, but I also occasionally work with others. I feel comfortable with this. Some people choose just one pantheon to work with. It is really a personal choice.
Initially, I think the best way to familiarize yourself with a god/dess is to read the myths related to the pantheon. Myths illustrate the personality of the deities that inspired them.
There are often herbs, stones, symbols and colors associated with each godform. They can be helpful in contacting them.
The goddess has many forms and aspects, Below is a list of goddesses from several pantheons and some of the things they rule over. This is by no means a complete list, these are just examples. Another way to look at the goddess is in her three aspects of Mother, maiden and Crone. These represent the three phases of life. These can also be related to three phases of the moon, New Moon (the maiden) Full Moon(the mother) and dark moon the (Crone.) The colors white, red and black also represent the three aspects of the goddess. White represents the Maiden, Red represents the mother and Black represents the crone.
The god has many forms and aspects, just as the goddess does. The god is sometimes worshipped in three aspects: The Sun King, The Green Man, and The Lord of the underworld. The colors corresponding to these aspects are yellow for the sun king, green for the green man, and black for the lord of the underworld. The god is often ignored in favor of the goddess by many pagans. Personally, I think both are equally important in the interest of balance. Both male and female energies exist in the mundane world, therefore, both male and female energies exist in the divine. Below is a list of some gods from several pantheons, and the things they rule over. This is not a complete list, these are just examples.