I have traveled to Mexico a couple of times.
Mexico is cool.  It is officially known as the United Mexican States.
How does it relate to the United States?
Well, the US resides along it's northern border, of course.  Size-wise, it the 6th largest country in the Americas.
How does it compare in terms of income to the US?
Well, it is quite a bit lower than the US.  It has a population around a third of the US's, with roughly 120 million people.
Do a lot of tourists visit Mexico?
Yes, but the high crime rate deters a lot of visitor's.  Mexico has gone through a period of increasing crime-rates, especially in urban centers.
That's sad to hear. No wonder most of them try to start a new life in the US. How many murders occur there every year?
I am not sure, but the increased drug trafficking and organized crime cause most of the violent crime in the country.