Choose an atlas that has the information you are needing to find out about. Determine the layout of the atlas, study the key to the maps, use the table of contents and reference the index. If you can get familiar with atlases then you will find that they are pretty easy to read and very useful.
1 Additional Answer
An atlas is a large group of maps. To use an atlas, you would determine what city, state, or country you like to look at. Use the glossary in the atlas to determine what page to turn to in the atlas.