When working on your assignments, you may consult: the instructor; the TA; either of the textbooks; any materials that the instructor distributed.  You cannot use any other sources without first getting permission from the instructor.

In particular, you are not allowed to search the internet for help with your assignment.  

And you are not allowed to talk to anyone else, other than the instructor, the TA, and your partner (if you have one) about how to solve, or even begin to solve, any problems on this assignment.

Here is a page, written by an instructor at St.George, that explains some of the subtleties of plagiarism.  The main point is:  even if you are not blatantly copying another student’s written assignment, you still might be in violation.  For example, if another student told you a key idea required to solve a problem, and then you use that idea to complete your assignment – it's a violation.  Even if this happens while you are working together, and even if you also told that student one of your key ideas.

When you submit your assignment, you are implicitly stating that all the ideas in that assignment are yours. 

It is OK for a group of students to get together to study the course material and help each other understand it.  It is OK to work together to solve practice problems.  But when students start discussing how to solve an actual assignment problem, then this will usually result in plagiarism.