I like to tag profound truths to practical daily realities, so I have defined mercy as "giving grace to those who give you grief". An equally practical tag line is this "trying to be helpful to those who are being hurtful to you".
Several Biblical examples of where Jesus gave illustrations of mercy can be found in:
The parable of the unmerciful servant - Matthew 18:21-35
The story of the Good Samaritan - Luke 10:25-37
Straining a gnat and swallowing a camel - Matthew 23:24-24
I recommend those for further study to help you wrap your head and heart around this important Kingdom virtue of mercy.
But here is powerful contemporary illustration of what mercy looks like:
Meditate on how their merciful response impacted their community and the world.
Ask the Holy Spirit to search your heart and measure your mercy quotient.