Where do your characters live?

Your characters need to be placed in a setting for your story to work. As a science fiction writer, one of the attractions of the genre is the chance to invent the complete world my characters move through.  

How much you need to know about your setting depends on the type of story your're writing.  If you're writing a tense claustrophobic murder mystery set in one town you may need to draw yourself a detailed map of that town.  If, like me, you invent whole planets, you'll probably need to draw a map of the continent/island your characters are on and  invent all the features there.  

You need to know the geography: towns and cities, rivers and lakes, agricultural areas, wilderness. You'll need  to know the climate.  In Panthera : Death Song the action takes place on a huge continent lying across the planet's equator.  Most of it is tropical rainforest, and the climate is hot and frequently wet.

What's the social geography of your story?  What are the societies/classes/clans of the people?  What occupations do people have, is their world high or low-technology?  Even on Earth, there are vast variations in technology levels and use in different countries.

Look at pictures for inspiration,  or take evocative names from wine bottle labels and write about the places they suggest. Setting is not just a frame for the characters; a well-drawn setting is often a character itself.