When you're out with your child, have them look around. Ask them to consider if they are similar or different from those around them. It's a tough question because it's really a trick question. More often than not, we are able to identify ways that we are different, but also many ways that we are similar.
Discuss that being tolerant and accepting of others means recognizing that they have a different opinion or lifestyle than you, but still respecting their point of view. Note for them that we do not have to agree with someone in order to accept them! We are all different from each other and that can be quite interesting and a great thing!
Discuss some ways we can be different from one another. Examples might be nationality, where we grew up, religion, interests, looks, style, opinions, gender, skin color, and so on.
Have your child consider what it might feel like if someone didn't accept THEM for who they really are. Everyone deserves to be accepted and respected as a human being.