nin：just say to elder or somebody in respect. ni:say to someone who has the same age as you.

ni (你)，while nin（您） both mean "you" but there is a heart = 心 in the character 您 So it is used in front of the old ppl or superior guys. In front of friends,we use 你

nin: is used when you talk to someone that is older than you or when you want to show respect to that person ni: is used to people in your age or just people you are familiar with I don't know Portuguese, but compared to Spanish, nin=usted, ni= tú

nín:you(polite form) For example, After you, please!请您先走(qǐng nín xiān zǒu)。 nǐ: you(used for most events) For example, 你好吗？（nǐ hǎo ma）你忙吗？（nǐ máng ma ）

Ola,amigo... there are some relevant words in Portuguese that can explain these two words"ni&nin" ni---tu nin---você that is...Nin（您）is used in a more respectful way,just like 您从哪儿来? Nin2 cong2 na3 er2 lai2? =De onde você é? De donde es usted? nin2=voce=vous=usted ni3=tu