Skimming and scanning are two reading technique which is used to quickly find or understand information from a text. But they shared different purposes.

What is Skimming :

Skimming is a reading technique which is used to get the gist of a text.

Example: If we  received any lengthy email or massage from anyone we can skim it to understand the basic topic and important point before going back to read it in details.

       If we want to read any article or paragraph we can skim it though heading and subheading to determine if it's worth our time.

What is Scanning:

Scanning means to search specific information or keywords from a text not by reading the full text. It's generally happened when you know what you are looking for.

Example: Suppose you are looking a specific word in a huge article. Rather than you read it fully you can just scan it for the word you looking for.

     Imagine we have a book of 200 page and we want to find the exact name who wrote this book. Now without reading the whole book we can just scan this book to find the writer name.