To give you a better understanding, I will provide an example. If you search for "acne", you will very likely see pages from established health websites, detailing information about acne, its causes and treatment. You may not be able to find what you are exactly looking for in those pages, so you will use more keywords to narrow down the results. Your next query could be "home remedies for acne". The results are more targeted, compared to the previous where the results may be very wide in scope. Basically, longtail keywords are highly targeted phrases. It is generally easier to rank for longtail keywords because 1.) there are fewer pages and 2.) there is less competition.