Stereotyping is to believe/think/say groups of people are the same when they're not.
The first example of stereotyping is:
Americans eat lots of KFC. I disagree because lots of Americans are fit and healthy and I see lots of Americans playing fit sports and running.
The second example is:
Asians are bad drivers. I disagree and agree at the same time because they are good drivers in their country but bad drivers in our country. Some Asians are good at driving on our roads. Their challenge is to learn our road rules.
The third example is:
All boys play rugby and girls don't. I disagree because lots of girls play rugby for winter sport but some girls don't like to play rugby.
Overall I think stereotyping is a way of making people think they have to be exactly the same as everybody else. It is a way to tease somebody as if they can't change that thing they are being teased about.