How to calculate zakaat

Q: I'd like to know how to calculate zakaat. I am 25 years old and have never paid it as I don't know how to calculate it. I do tutoring for 2 children, I have some shares, I have some money in my bank account and I have money in a money box but I don't know how much money I have in that money box. I also have some gold jewellery of which I wear some of it but not all and I don't know the value of it.

Is it true that you have to also pay zakat on clothing that you have not used in over a year? Please assist.