How do you write equations for these?

In response to your edit, it's a redox reaction. Since both of your anions are chloride, the cadions aren't going to "switch" like normal. Instead, they're going to go to their other oxidation states. Tin has oxidation states of +2 and +4, and iron has oxidation states of +2 and +3. Therefore, tin will go to +4, and iron will go to +2, making it the reaction you posted in your edit.