Think of any man-made object.
Now how do you know it's purpose?
I would say, by what is does...it's function.
What was it made for? (to clean, to hold, to entertain, to power, to connect, to instruct, to educate, etc..)
Pick a different man-made object now; one that you have no idea what it does.
What will you do now to figure out it's purpose?
Put it through tests and trials?
The easiest solution:
If you know who made it, you could ask them.
Do you know your purpose?
Ask your Maker.
What is my Purpose?