I heard that the Samsung J's take two SIM cards, and i want to know why is that? And is every phone capable of having two SIM cards ...? Also, what are the beneficials if I was to root my phone, Samsung J7?
Welcome to Android Central! The J7 is a dual SIM phone. Not all phones are dual SIM -- it's more common for world/international phone variants, and very uncommon in the West. The advantage is that the user can insert two different SIM cards, and therefore swap between two different carriers.