Currency symbols are characters written or typed in a specific arrangement alongside the numerical values of a currency amount, to denote the kind of currency in which the amount of money is held.
An example would be the dollar sign ($), which is placed at the beginning of the numbers which describe the amount of currency in question, despite the fact that in most languages the word “dollars” follows the numbers when spoken. Many currencies have their own symbol but not necessarily all do.
The symbol makes it easy to recognize the kind of currency being described in any context, and it saves space when currencies appear on signage and in tables and charts. Not all currency symbols have been around very long.
The Euro, being a new currency, had to be added to the Unicode character list and computer operating systems, as did the new Indian Rupee symbol in 2010. Most currency symbols will have a keyboard shortcut so that they can be typed.
Currency symbols appear most often in front of the numbers which are the amount of currency being discussed, but some, like the Cape Verde currency, appears in the place where the decimal (or comma, in some conventions) would be for other currencies.
Incidentally, the Cape Verde escudo currency uses the same dollar sign that you are likely familiar with, but the symbol represents the escudo when used in that unique position. Some currency symbols appear after the numbers being discussed, the way that the sign for cents (¢) in the US appears after numbers when only amounts smaller than a dollar is being discussed (99¢).