The suffix "-st" is commonly used in English to form the superlative degree of adjectives. It indicates that something has the highest degree of a particular quality among three or more items. For example, in the word "fastest," the suffix "-st" shows that one thing is faster than all others in a group. Additionally, "-st" can also be found in ordinal numbers, which indicate position or order. For instance, "first" and "second" are examples where "-st" is used to denote rank. This helps in organizing items or events in a sequence, such as in a race or a list of achievements.