Americans are generally known for liking a lighter coffee brew than their European counterparts, so when the US Armed Forces in WWII poured hot water into their espresso shots, the café Americano was born.
If you like the flavor and freshness of espresso, but want a lighter body and less bitterness, the Americano might just be your drink. To make an Americano, pour a shot (or two) of espresso straight into a large cup or mug. Then add hot water (up to 4 ounces). The general ratio is going to be 1/3 espresso to 2/3 hot water, but you can experiment to find the intensity you like. You can also add milk or cream on top.
If you want the Americano style of coffee, but want to preserve the crema (that thin layer of foam on top), you can also try the Long Black. In this case, you would pour hot water into your glass first and then add your shot (or two) of espresso.