All types of data are stored inside the computer as numbers. Each character in text is stored as a number that represents the character. In personal computers, a common way to do this is to use ASCII - the American Standard Code for Information Interchange. This is just a standard for linking the numbers to the characters - e.g. 65 is A, 66 is B, etc. The range of characters that the computer can display is called the character set.
is represented by the ASCII code
Note that not all characters are visible - there are things like spaces, carriage returns and line feeds that are invisible on a web-page. Notice also that upper and lower case letters have different codes.