They don't speak English , man.
Then it's your job to learn. I doubt anyone in your home country speaks a word of Polish.
3 moths are little cheaper. Wat does it mean "3-months up to 18 stops, whole network" I guess that you can choose specific line and then your monthly or 3 months ticket is valid only there. But it says whole network. So who from Poznan can explain that?
Easy enough - you nominate a specific stop, for instance Wroclawska tram stop (in the heart of the city). That ticket then allows you to travel on trams (and I think it allows interchanges to buses) up to 18 stops away from Wroclawska. You can go in any direction with such a ticket - the idea is that you can't travel beyond the 18th stop from Wroclawska. I'm just not sure if such a ticket allows you to change to a bus or not - I think it does, provided it complies with the 18 stop limit.
And as a student perhaps you're allowed to pay 53,50 zł. You should read terms and conditions because some cities accept discounts for international students having card ISIC or EUR26. Except if you have Polish student's card - then you can use cheaper fare for sure.
Poznan - up to age 26 with ISIC or a Polish student ID card allows the use of discounted tickets.