Is there anyone who has an explanation of the strain issue in Strength of Materials?

I have an exam tomorrow and need explanations on the subject of strain ? 

What part of it do you not understand? Are you looking for a tutorial? 

I needed some examples, explanations and some advice to solve

https://nptel.ac.in/courses/113107078/26

https://nptel.ac.in/courses/112107146/9

https://www.google.co.in/search?q=nptel+lecture+on+stress+and+strain+in+materials&ie=UTF-8&oe=UTF-8&hl=en-in&client=safari

thank you @Ramani Aswath