How to calculate the P-value?

Ok, so I'm a little frustrated right now, because I need to know how to calculate the p-value for a t-test. All the videos I've seen online suggest doing it with the help of a calculator, but I don't have a calculator with that function. (I do have a Casio Scientific Calculator, if anyone knows how I can calculate it on it!) So how do I calculate the p-value for a t-test?