Difference between kita and kami!!
Kita means we/us but includes the speakers/persons in question you are talking to, while kami means we/us too, it does not include the speakers/persons in question you are talking to.
Halo, kami akan pergi ke penjual makanan. (Hello, we are going to the food vendor)
If you use kita in that sentence it will be wrong, because you aren't referring to yourself, family, friends, or classmates. In some cases, with kita it can also include god and politicians!!
Buku kita sudah hilang. (Our book has been gone.)
If you use kami in that sentence it will be wrong because you aren't referring to any one person in the sentence, you are referring to multiple people's book.
Examples (Try em out!!):
Kita? Lo aja kali, gue enggak. (Us? Please, it is only you, not me.)
Berkatilah perjalanan kami hingga pulang ke rumah. (Bless our trip until we reach home.)
"Kami" refers to you and your friends while talking to another person outside the scope of "Kami". While, "Kita" refers you and a group of people you are talking to.
For the second sentence it is actually possible to use kami if you say it to, say, a teacher:
Pak Guru, buku kami (para murid) sudah hilang.
Sir, our (the students') book has been lost.
Continued by the teacher scolding the students for losing the book.
But this post is very important. Even some native Indonesians are losing the distinction and uses kita for everything, which makes me really uncomfortable.
For the first example it's also possible to use "kita".
If the persons that you are talking to are also accompanying you to the food vendor.
Both examples can use kita/kami, depending on context.