Here's a list of all th shortcuts. Just choose the one that works for what you want to grab. I always use Cmd+Shift+4 so I can drag to select the area I want.
Of course I'm still used to a PC. The MAC IS AWESOME. When I hit shift, control4 it automatically saved to my desktop, I didn't have to paste it or save it.
Yeah! I know.....I really love my mac too. Another program I use to do screen shots in Skitch. It is a free app for the Mac store or google it. It is another great way to get screen shots and it saves to a folder. I use it too.
I found an app called Gyazo. I LOVE it to share the screenshot with others. The app uploads the screenshot on their server (so, obviously, you wouldn't want to take screenshot of anything sensitive) and gives you the link. You can share that link with others. You can delete the screens later if you don't care for them.
I use an app that sounds very similar to the one Ripal mentioned. It's called Captured. It's great for getting a quick screenshot of something that you want to share in a forum cause you have an IMG link immediately. And, it also saves the screenshot to your desktop.