Collaboration in academic settings is generally a good thing. However, you must be clear about two issues when using other people's work: copyright, and plagiarism.
Copyright is a legal issue: does someone else own this image or video or phrase? The details of what exactly you're allowed to use and in what context aren't trivial. In this age of the internet, it's particularly easy to grab an image or whatever off a website somewhere, and use it in your presentation or paper. However, unless the creator specifically grants you permission, that's usually illegal. (The most often used academic exception is called "fair use", which can allow non-profit academic use of small portions of copyrighted works.)
Plagiarism is an ethical issue: implying (even without intent to mislead) that something is your work when it isn't. Whenever you submit academic work, you must make it clear what you did and what is due to other people. Be sure you understand this: serious infractions can get you flunked from a course or kicked out of school.
From Marlboro College's "Policy on Academic Integrity" :
"It is the responsibility of all students to inform
themselves of the of the content of Marlboro College's
Statement on Academic Integrity which describes
student's responsibilities in ensuring the academic
integrity of their work."
In any academic paper or computer code, you must "cite your sources" whenever you are borrowing, directly or indirectly, from a book, website, or another person. How you do that depends on how formal your work is, and what your audience (including the faculty member looking at your homework) expects.
Google "how to cite" to find online engines that can format your citation in a variety of spiffy ways.
For a CS (computer science) plan paper, each chapter typically has a formal bibliography of sources. For homework, any clear way of indicating the author or URL of work you are using is OK.
Many software packages and artistic works now have "free" licenses that encourage people to use, share, modify, and re-distribute them. There are a variety of such licenses for various sorts of materials including "open source" for software and "creative commons" for artistic works. Sometimes these are called "copyleft" rather than "copyright" licenses since they are designed to ensure that others can re-distribute the work, rather than prohibit them from doing so. These sorts of materials are still subject to copyright and plagiarism issues. When you use (or re-use) them, please make sure you do so within the appropriate legal and ethical rules.
Here are a few starting points for more information.
In Jim's courses, collaborating on homework assignments is generally fine - just make it clear who did what when you submit the work. Likewise, it's often perfectly reasonable to use open source software as a basis for your project - as long as it's clear what your contribution is, and that the work you've put in and the understanding you demonstrate is appropriate to the assignment.
Usually what is and isn't OK will be clear from the assignment. If you have any questions at all, ask.