Hence the confusion among beginners and switchers from Windows, where the corresponding key is Control.
Even experienced mac users sometimes get confused when they see or hear 'Command' mentioned. Some call it 'the apple key' after the Apple icon shown on the key together with a squiggly rectangle.
In Windows you press Control and type S to save a document. On a Mac you press Command and type S. Most other standard keyboard operations are a combination of Command and one of the letters of the keyboard, for example, Command+P - to print, Command+Z - to undo.
If you touch-type, I suggest using the thumb of your left hand to press Command: move it slightly away from the Space bar, press and then type the letter of the shortcut.
The Control key is also present on Mac keyboards but it is not used as widely as in Windows.
Wikipedia has an article Table of Keyboard Shortcuts that shows which shortcuts on a Mac correspond to which in Windows. In iWork, a list of available shortcuts is under the Help menu.
If you want to use the Command icon ⌘ in your document, go to the Edit menu and slide down to Special Characters. When the character palette opens, click on Symbols > Technical Symbols and drag the icon from there to your document.