What`s the different between "in the iveninG/morninG" and "in the iveninGS/morninGS"

First notebook entry: Introducing myself As I`ve already written, I`m a cosmetologist. To learn more about new technologys, cosmetic drug and so on i have to read foreign literature. Some time I travel abroad. So i need a good english level for it. Few words about myself. I`m merried, have 2 dochers 1 and 2,5 years old. I like cats and dogs but becouse of them we can`t afford to have any pet - children may hurt them. So, that`s all for a while. I`ll be happy to have an answer from you.