Mean is the average of all the data/scores, which can be obtained by adding all the data then dividing it by the total number of scores.
Mode is the most frequently occurring score within the data, which can be obtained by arranging the data then find the most repeated. There can be more than one mode.
The median is the middle/center of the data, which can be obtained by arranging the data then finding the one in the middle. If there is no single score in the center, find the mean of the two central numbers.