"Do your work."
Translation:अपना काम करो।
Ummm.... It is sort of complicated for me to explain. But let me try....
अपना is used to express the belonging of the subject.
Eg आप अपना काम करो। (You do your work)
वो अपना काम करे। (He shall do his work)
आपका would be used if someone else was doing the work of person in front of me.
वो आपका काम करे| (He shall do your work)
To say You do his work. आप उसका काम करो|
I hope this clears things up a bit
अपना is not a form of आप.
It is a pronoun which always refers to the subject of the sentence. Since this sentence is a command, the implicit subject here is 'you'. That is why the अपना in this sentence means 'your'. If you want, you can also explicitly include the subject - तुम अपना काम करो।
To see how अपना doesn't always mean 'your', consider the sentence मैं अपना काम करता हूँ। The subject of the sentence is मैं (I) and so, अपना here means 'my' and the sentence translates to 'I do my work'.