You’ve already seen “dekiru” as a verb meaning “to be able to do”. But when used in the past tense it also means “to have completed”.
This might seem a little confusing, but it actually makes a lot of sense. To be able to do something means being able to complete whatever tasks are associated with that thing. From that perspective it makes a lot of sense to use the same verb for “to be able” and “to complete”.
出来る = できる = to complete; to be able to do
書く = かく = to write
Yellow: Turned it in right before the teacher walked into class.
Blue: That was really cutting it close.
Blue: What’s wrong?