This is the 4052nd most frequent Turkish word.
gerek
"Necessary" or "need."
The word 'gerek' is used as a verb here indicating necessity, translated as 'need'.
Öğrencilerin başarı için çok çalışması gerek.
Students need to work very hard for success.
Here, 'gerek' is again showing necessity but is followed closely with a condition if-clause.
Başarılı olmak istiyorsan, özverili olman gerek.
If you want to be successful, you need to be dedicated.
In this context, 'gerekli' is derived from 'gerek' and is used as an adjective meaning 'necessary'.