In the Widget Framework, a template is a special kind of section. A template differs from an ordinary section in the following ways:
It is named according to a special convention that identifies it as a template rather than an ordinary section.
Instead of containing actual content (teasers and so on), it contains widgets. The widgets define how content is to be presented on section pages and on content pages.
It is stored in a blueprint rather than in an ordinary publication.
This chapter will tell you how to create and edit templates. It also contains explanations of how templates work, and how they are related to ordinary sections and content pages. It is probably a good idea to read through the whole section and then to try following the instructions in Creating a Template.