By examples of where I was a leader? Though seriously, if you don't have an example don't worry... draw up a list of "skills a doctor should have"... should be easy and you should be able to come up with over 15 in under a minute or two. Now pick a few of those skills you know you have and can demonstrate... and write about that So long as you show suitability to be a doctor, you should be okay..
I was the Managing Director of the young enterprise team at my school! Had to use a variety of skills; decision making, communication, leadership, management skills, team work etc...
I didn't, the only one I could think of was the rather lame "I led my DofE team for a leg", and I figured mentioning it might do more harm then good. I did get asked about leadership at interview though, and gave the lame answer above. So I guess you can always think of something small and blow it out of proportion...