I think it is useful to take a step back from math when dealing with logic, and take examples from the real world. My favorite implication example is "If it rains, Bob comes to the office with an umbrella". Another even cleare is "If you are standing right in front of me, then I see you".
There are two issues that I think you're raising:
- How to prove that this implication actually exists, that is, prove that in EVERY rainy situation Bob comes to the office with an umbrella. Or to prove that EVERY time you're standing right in front of me, I can see you.
- Use the implication (which we know to be true) to infer something (either about the weather or Bob bringing an umbrella to the office).
Let's focus on 2 (which helps for 1).
If we know that an implication exist, then the easiest way to use (the so called "modus ponens") is: "Hey, it's raining. Then I'm sure that Bob is coming with an umbrella, I don't even need to check, cause I know that this fact is GUARANTEED by the fact that is raining". No sweat. The countrapositive, or "modus tollens" is less intuitive, but not hard to grasp with an example: "Hey, Bob does not have an umbrella today. Could it be raining outside? Of course not, otherwise he would have brought an umbrella". In terms of the other example: "Hey, I don't see you. Could you be standing right in front of me? Well, no, otherwise I'd see you". Of course, we are not assuming invisibility or other kind of esoteric stuff here...
Now that we know how to use an existing implication, let's think about 1. How can I decide that an implication between two facts actually exists? Well, in math we can use logic (which uses previous results, probably based on previous implications). In real life we "trust" our intuition, or trust a large number of experiments showing the same result. Unfortunately there's no universal SURE law in real life, only "strongly" believed ones. But if we focus only on the observed past, then sure laws exist, based on the collection of all experiments.
Back to Bob. How can we prove that the implication "it rains-> he brings an umbrella" exists? Well, we stalk Bob and observe him through all his work days. But that's expensive. So we can cut down the costs a bit. Two ways:
- We stalk Bob only when it rains, and check whether he's bringing an umbrella (pass) or not (fail).
- We don't stalk Bob. We just see him at the office and check whether or not he has an umberlla. If he does, we don't do anything. If he does not, we check if it's raining (fail) or not (pass).
Now, 1. seems the most obvious way, and it clearly looks correct. On the other hand, 2. seems weird. How can a pass support the implication? After all, we only checked that he never has an umbrella when it's not raining, but we do not have any guarantee that he did bring an umbrella when it was raining. Or do we? Well, we actually do! In fact, there are two possibilities:
a) It never rained. In this special scenario, Bob never brought the umbrella, we always checked (every day). It is a not so interesting scenario since the implication is probably going to be useless. All the days were the same (it never rains!), so there's no distinction to make. We may assume that the implication is true, since we have no grounds to reject it.
b) It rained at least some days. Well, it certainly did not rain when he did not bring the umbrella, cause we checked. Then it must have rained when we did not check. But that's precisely when he brought the umbrella. Therefore the implication DOES prove right.
Well, I'm getting long here, so I will stop. In short, I think real world examples are easier to grasp. Also, regarding what your student said ("you are giving me one false statement, and asking me to prove another false statement, I don't understand") it could help him to mention that a "false" statement can be seen as another statement that is "true": the statement where I affirm the opposite thing.