It converts a number into its ordinal form, such as converting 21 into "21st".
It correctly applies "th" to 11th, 12th, and 13th rather than incorrectly using "st," "nd," or "rd," since these are a well-known exception in English ordinal rules.
Numbers ending in 1 use "st" (like 21st), ending in 2 use "nd" (like 22nd), and ending in 3 use "rd" (like 23rd), except for the 11th-13th exception.
Yes, the tool applies the correct ordinal suffix based on the absolute value of the number you enter.
All other numbers use the "th" suffix, such as 4th, 5th, 100th, and so on.