Hi foxwhite,
Good question. Let's begin:
'Us' is used only with a preposition. Come with us, sing to us, dance for us, be nice to us, get away from us, he loved us, I do not want him to sit with us, he sat with us, etc. It is plural, so it must refer to more than one person.
'Our' is a possessive pronoun. It means the speaker and at least one other person own something - 'this is our house,' 'that was our breakfast,' 'he is our friend,' 'our country is beautiful,' etc.
'Ours' is a possessive adjective. It modifies an object to say that it belongs to the speaker and at least one other person. 'This house is ours.'
You must be careful not to confuse 'our' and 'ours'. You could say 'our house is ours,' but not 'ours house is ours.'
Our house = The house that belongs to us
Ours = belonging to us.
'Our' always precedes the noun, and 'ours' always follows the verb 'to be'.
And finally, we!
'We' is a personal pronoun which indicates the speaker and at least one other person. It always precedes the verb and says something about the speaker: 'We like to dance,' 'We have to go,' 'we are happy,' 'we will eat cake.'
I hope that helps! If you have any other questions, you can send me a message and I will do my best to explain more!