How do we know when to reject Ho or fail to reject Ho (null hypothesis)? Can you give a real life example of how this concept is applied?

How do we know when to reject Ho or fail to reject Ho (null hypothesis)? Can you give a real life example of how this concept is applied? To support your research and findings in your initial post – Give an example using a p-value and level of significance (alpha) where you would reject the null hypothesis and where you would fail to reject the null hypothesis.