If you are a new Mac user, you may want to learn: what are the meanings of these symbols? Let Have a quick look of these symbols;
alt 
- (Option Button) - This button is generally using on keyboard shortcuts like; Sleep, Force Quit etc...
cmd 
- (Command Key) - Gives the command function. When you press to  cmd + X for example; That will cut the item you selected. It has the same function of Ctrl in Windows
fn (Function) - This button is generally using on MacBooks. Because of the keyboard size these laptops, fn key is generally using in all applications and shortcuts.
shift 
- (Shift Button) - Like everyone knows, when you are writing a text, It give big characters while you are pressing on shift button. Another function is; It's using in keyboard functions like; Full Screen View in Firefox, Empty Folder, New Folder etc...
caps lock 
- It's Enabling/Disabling Capslock function.
