It can be contrasted with skimming, which is reading quickly to get a general idea of meaning.
Example
A learner taking a reading test needs to scan a text on population rates quickly to find out if a series of statements about the population figures are true or false.
In the classroom
As the above example shows, scanning is a specific reading skill which is often used in combination with others such as skimming and intensive reading. Learners need to learn different ways and understand that choosing how to read is an important step in building reading skills.
See also:
https://www.teachingenglish.org.uk/article/skimming
Further links:
https://www.teachingenglish.org.uk/article/theories-reading-2
https://www.teachingenglish.org.uk/article/using-stories-classroom
https://www.teachingenglish.org.uk/article/unit-4-reading-skills