Here is some basic information on the four types of scales that you're going to want to be familiar with for this course. It is important to know the difference between these in order to appropriately apply statistical tests later on in the course.
Nominal Scales.
Nominal scales are easy. Just think of social security numbers. They really have no meaning. They are just a number assigned to each person for identification purposes. There are other examples of this, like numbers on football jerseys or highway numbers or locker numbers. Just remember, these numbers don't mean anything, hence their name "nominal" meaning in name only.
Ordinal Scales.
Ordinal scales have some order. We can now use terms like "more than" or "less than" in describing the data from an ordinal scale. We can rank objects on an ordinal scale. We can rank people by height, like Joe is tallest and Ethan is second and Saul is third. We don't know by how much in this type of scale, but we do know order.
Interval Scales.
Interval scales are those where the difference between the values in the scale are equal. For example, height as measured in inches. An inch is an inch and 2 inches is twice one inch. If Joe is 59 inches tall and Ethan is 57 inches tall and Saul is 56 inches tall we know there is a 2 inch difference between Joe and Ethan and this is twice as much as the difference in height between Joe and Saul. Test scores also tend to be interval scales.
Ratio Scales.
Ratio scales are the same as interval scales (there are equal units between points on the scale) but also have the characteristic of having an absolute zero point. This absolute zero points must represent that the variable being measured has NONE of whatever it is. With the addition of this absolute zero point we can make statements like "twice as long" or "half as fast". Time is an example of a ratio scale. If we are measuring the time it takes Joe and Saul to run a mile and Joe runs it in 5 minutes and Saul runs it in 10 minutes we can say that Joe is twice as fast as Saul.