Since computers only use numbers, they use number codes to represent characters. For example, in ASCII, the number 65 represents the letter 'A'. The computer knows, when working in ASCII, to put the glyph for 'A' on the screen when it sees the number 65. The glyph can change shape slightly depending on the font that is used, if it is bold or in "italics", etc. But it is still stored as a 65 in the computer, that does not change.