What does might makes right mean?

'Might makes right' is a very old saying that meant and means that if you have the power to defeat you can force your will upon those you have power over.

Examples would be:

Germany before WWII, is it right to sterilize or kill people because they are different then you? Of course not but the "Nationalist Party', (later the Nazi Party), had the power over the people and they did it.

A simple one would be:

Your Parents send you to bed a 8 o'clock. Is it right that you should go to bed at 8 o'clock? Maybe not, but they have the power to set the bed time.

So as with any power it could be misused or it could be used for good as in your parents making sure you get enough rest to be healthy, able to learn and ready to grow.