A statistic is any number that describes a group of objects. There are two main categories of statistics, descriptive and inferential.
Examples of Descriptive Statistics
The class did well on its first exam, with a mean (average) score of 89.5% and a standard deviation of 7.8%.
This season, the Big High School Hockey Team scored a mean (average) of 2.3 goals per game.
Examples of Inferential Statistics
According to our recent poll, 43% of Americans brush their teeth incorrectly.
Our research indicates that only 33% of people like purple cars.
In these last two examples, the researchers have not studied all people, they have studied a small group of people, and are generalizing the results to lots of people. This is known as inferential statistics, because you are inferring properties about a large group from a smaller group. As a statistician or a researcher, it is your hope that this smaller group is representative of the larger group, and that the two groups behave the same way. If they do not, then your inference may not be correct.
If you merely want to describe the data that you have for one single group, then you are using descriptive statistics. If you want to say something about a larger group, or you want your reader to infer something about a larger group, then you need to use inferential statistics. It is important to understand the difference between these two because how you use a statistic depends on what type of statistic it is.
Begin looking at places that produce stats.
Here is a general checklist to begin with:
Government Agencies
Federal government
state government
local/city government
Non-Government Organizations
Human rights organizations
Women's rights organizations
Children's rights organizations
Academic Institutions
Databases like Opposing Viewpoints
Private Sector (usually comes with a fee)
Businesses
Firms