Descriptive statistics simply describe what you have found when carrying out an investigation. They make no attempt to go beyond the data contained, and they do not explain what caused the result. They are simply a means of presenting the data in the clearest way possible.
"Statistics: The only science that enables different experts using the same figures to draw different conclusions".
— Evan Esar (1899-1995), American Humorist
The two main calculations of descriptive statitics in psychology are Standard Deviation and Measures of Central Tendency.