This guide are for Samsung Galaxy Ace users that doesn't know yet how to take or capture screen image from the phone. When I got my Ace S5830 I have the same scenario too, then tweaking up and tried to press several button combination. And fortunately I figured it out after trying several attempts pressing the HOME button with the BACK button (touch sensitive buttons - on the left and right of HOME button). Bingo! that's how we can take and save screenshots on our Galaxy Ace.
An example of a screenshot on my Samsung Galaxy Ace
Navigate to the screen you want to take screenshot ( homescreens, menu's, or game screens, etc ) press and hold the back button in the right corner while holding it, press menu key once and a notification will say the screenshot is taken. The images will then automatically save in the image file folder called "Screencapture"
That's it all!