It is used to form nouns that indicate:
* A person who practices or believes in a particular activity, art, or philosophy.
* Examples: artist, pianist, socialist, feminist
* A person who specializes in a particular area of study or work.
* Examples: physicist, chemist, biologist, historian
It's important to note that "-ist" is not a verb suffix, though it can be used to form verbs indirectly. For example, the noun "scientist" can be used to form the verb "to scientize," which means "to apply the principles of science to something." However, this is a rarer usage.