Student or Learner
Is there any idiom or expression ,when i want to say i finished from one of them ,for example,i have 5 exams to write and i finished the 1st one.
i think there is an expression "one down..." something like that!
In the case of your exams, it would be "One down, four to go." I'm not sure it qualifies as an idiom, but a very common expression.
It could be used ironically in the case of some practically insurmountable task. "Great, that's one down, only nine hundred ninety-nine thousand to go."
[native speaker, not a teacher]