How long do you want it to take?
Any answer, including that it's simply not possible, is reasonable under the right circumstances. Consider the two extremes:
If you want it to be easy: A craft capable of space travel would almost certainly need something comparable to a computer, capable of storing and processing large amounts of information. A sufficiently advanced computer might be designed to teach an intelligent but ignorant 'user' the basics of its creators language, technology, and culture. There are certain concepts and patterns that are universal. The prime numbers and the chemical elements are frequently-cited examples. A very smart human and a very sophisticated computer could work together using these first principles (and a certain amount of 'hold up an object, say its name') to establish communication. The amount of time needed would then depend only on the level of understanding desired. Simple concepts might take only hours or days to grasp, but a full understanding of human culture is already the study of a lifetime, and an alien one would be no less extensive.
If you want it to be impossible: Consider Linear A, a written language of the Minoan civilization. To this day, we have no idea how this language works, despite centuries of scholars, linguists and even cryptographers studying it. We just don't have a large enough sample of the language, and it seems to be completely unrelated to other languages of the time, meaning we have no basis for comparison. It's likely we'll never be able to read it. Without a readable language, anything we might say about an alien culture is at best an educated guess. And per Clarke's Law, alien technology might be effectively magical to us, making use of properties of physics that we don't even know about yet. At best we would be able to describe such things in general terms - 'this probably stores information', 'this is an engine, I think', 'this is some kind of power source'. A human would be unable to replicate or repair such technology, and might or might not be able to operate it, if it were already functional.