What this suffix does
The suffix -ist creates nouns that name a person in relation to an activity, doctrine, instrument or field. From "art" you get "artist"; from "guitar" you get "guitarist"; from "piano" you get "pianist".
It can indicate a profession, a belief, or simply someone who practises or is enthusiastic about something: scientist, journalist, tourist.
The Spanish speaker advantage: -ist = -ista
This suffix is identical in English and Spanish, and the cognates are direct:
artist = artista
pianist = pianista
tourist = turista
specialist = especialista
journalist = periodista
Almost every Spanish -ista word has an English -ist equivalent. The only formal difference is that Spanish uses -ista for both genders, while English uses the same -ist form for everyone.
-ist also signals beliefs and ideologies
Beyond professions and instrument players, -ist marks someone who follows an ideology or holds a belief:
capitalist, socialist, optimist, pessimist, realist.
These -ist words usually have a partner in -ism: capitalism, socialism, optimism. Learning them in pairs gives you two words at once.