How do I determine if this argument is valid?

Question

I'm studying propositional logic the section on "valid arguments".

A self-assessment question reads

"Show whether or not the following argument is valid"

$\frac{P}{C}$

I don't know what function to apply to P to calculate C.

The solution in the back of the book shows the following truth table:

Variables   Premise Conclusion
P       C      P        C
F       F      F        F
F       T      F        T
T       F      T        F  <--
T       T      T        T

So the conclusion is that the argument is invalid because the premise is true and the conclusion false.

I understand that of course, but how do I calculate Conclusion? Do I just guess what it should be?

My teacher had the following to say:

If P is True, C is True. If P is False, C is False.

Swap it for 'Premise - I am thirsty' & 'Conclusion - I drink some water'

The conclusion is dependant on the premises. If there is only one, they > will never differ and a Conclusion will never be False, with a True Premise.

This answer flies in the face of the answer in the book.

I pointed this out to my teacher and got the following:

My understanding is that P is the only variable; C is the conclusion that represents what P might be i.e True or False, once evaluated.

So... in conclusion I find myself still confused