What this quote is saying is that you should embrace your life even if it seems like it isn't such a great life. As he goes on to say, people who are complainers will make even a paradise seem unhappy.
If I were trying to explain this with examples, I would try to point out how often (it seems) rich people are unsatisfied with their lives. I would try to find examples of people who were quite happy even though they didn't have a lot of material goods. I might also try to talk about what sorts of things make me happy and discuss the fact that those things (love, family, etc) are not the kinds of things that can be bought.
So, this quote is telling you to be happy even if you don't have material possessions. Try to think of examples like the ones I've mentioned.
Well that is a great quote. Thoreau was an incredible thinking. Here is an interesting picture of the guy, by the way.
To better understand the quote, make sure you have a good knowledge of all the terms being used in it. Most are easy, but a few could use explanation:
mean life: a hard, unpleasant life filled with challenges and obstacles.
meet it: do not run away from it.
shun: to not look at, to turn away from, to refuse to acknowledge.
hard names: insults (and curse words!)
So, in this context, take a look at the quote: "However hard or unpleasant your life is, do not run away from it; do not turn away from it or call it mean names."
This is a call to "rise up to the challenges." It is very easy to give into discouraging thoughts and events in life. It is very easy to just sit there and say "my life blows" and "why does everything bad always happen to me?" But that doesn't get you anywhere. The only course of action is to meet the obstacles head-on and overcome them.
For example, think about a man whose wife leaves him for a younger, more studly fella. He could very well sit back, get fat, and complain to anyone who will listen that about how his life has been ruined and how much it sucks. It could be an excuse to let his life run down...instead, it would make more sense to meet the challenge head on. Improve, reflect, and move on. That is a far more effective strategy.