How To Write ALT Code Symbols
The site has Alt Code, Uni code, Hex code and Decimal code values for special characters and symbols. The main page has previews of categories of Alt code symbols that you can select from the miscellaneous page. For each symbol there are at-least two types of codes available in the table. The easiest way to use these symbols is dragging and dropping the desired symbol or copy pasting it where you want it.
IBM came up with a way to input characters not found on keyboards, these were called OEM codes and were entered by using Alt + numeric keypad. Later on Microsoft introduced ANSI codes, which were like older OEM codes but distinct.
Now, Unicode is the preferred standard. However, compatibility issues with older OEM codes can limit the ability to input all Unicode characters using the same method.