Identify the random variable you are working with as discrete or continuous. A discrete variable has a countable amount of outcomes whereas a continuous variable does not. For example, the amount of siblings you have is a discrete variable, because you can count the number of siblings you have. The precise height of a given person is a continuous variable, because when calculated to the decimal place, the number of decimals is infinite.
Draw a two-sided table. Label the left side of the table "x" to represent your possible outcomes (given in your data set) and the right side "P(x)" to represent the probability of each outcome.
Write your data set down in the left side of your discrete probability distribution. If you were given a set of scores, you would write each score in ascending order down the left side of your table. For example, if the possible scores ranged from 1 to 5, you would make five rows, labelled 1 through 5.
Find the probability of each occurrence. Using the data given to you divide the total number of each outcome by the total amount of sample. For example, if 20 people out of 50 got a score of "1" on a test, divide 20 by 50 to get 0.4, or 40 percent. The number you get is the probability that a member of the group will get a "1" on his test. Each probability must equal a number between zero and one. When added together, the sum of all of the probabilities must equal one.