Q:

The difference between descriptive and inferential statistics

What is the difference between descriptive and inferential statistics?  How to identify from a sentence the difference of the two? 

A:

Descriptive statistic deals with describing given data, aiming to summarize a sample using measures of central tendency (mean, median etc.)  and measures of variabilty (standard deviation, variance etc.).  It "paints a picture" of the data where you can immediately see important information without having to work through thousands of numbers. 
Inferential statistics takes some given data (sampled by a population), analyses it and then infers properties about the whole population.  While the picture painted by descriptive statistics only takes up half of the canvas because you only have half of the data, inferential statistics tries to finish the picture.