Ordinals are numbers that express position in a series. By default, your word processor will convert ordinals into superscripts.
Superscripted ordinals have two problems. First, ordinals turn up most often in citations. The Bluebook and other citation authorities forbid superscripted ordinals (e.g., Bluebook rule 6.2(b)(i) (20th ed. 2015)). Second, superscripted ordinals are tiny and hard to read.
The best practice is to avoid superscripted ordinals. To do this, you have to adjust your word processor’s default behavior.