In Chinese mandarin,It seems that there were no obviously differences between Is Am and Are .the question was just yes or no,to be or not to be.we only use one word which was called "是(shi)" to express yes,and"否(fou)"or“不是(bushi)”to express no.
whats the different between This and That?We use "这(zhe),这个(zhege)" to express this.and “那(na),那个(nage)” to express that.
for example.
This one is mine.and that one is yours.
(这个)是我的,(那个)是你的。
It,它(ta)。
It doesn't mean that 它 is he,him or she,her.we never use it (它) to express people or someone.we just use it(它) to express the things or the animals,not the people.
hope you can understand what i've said.