A lot of the time when looking for information about a topic online I come across another university's resources that are publicly available. Some have a full listing of all the resources available for that course and others just have a PDF for one topic of the course. Can I read them or download them?
It is fair to say that if someone publishes something on the net then you can download and use it freely for personal use just as if you check it out from the library. At least, I've never heard any opinion that would challenge that.
Beyond that, you have to consider a few things. In the US, at least, authors gain copyright (all rights) to anything they create. If you don't find another statement to the contrary, then you have to assume that "all rights are reserved." To use something for other than personal use, for example republishing it in any form, you need permission: a license.
Some web resources are explicitly licensed with the terms carefully stated, such as through Creative Commons. Some are explicitly stated to be "Public Domain". But in the absence of such statements, assume that all rights are reserved.
It is easy enough to ask educators for permission to use their materials and most will give you some sort of license to do so. But you can still plagiarize people even when you have a license.
But for academic resources there is another consideration. If you found it, so can your students. So, reusing found exams and homework questions can be a bit risky. You can safely mine the resources for "ideas" of course, as ideas are always free to use.
I would like to say that you can freely link to found resources, as that seems sensible to me, but there are laws, especially in EU, that are bringing that idea into question. It is unlikely that you would be challenged for linking to an academic site, though you could possibly be for linking to a news site. The world of copyright is a bit weird and getting worse.
In the not too recent past, "fair use" permitted some limited reuse of the work of others, but only for specific purposes (and with attribution). One of the fair uses was scholarship, but that has been going away ever since the Xerox machine was invented, with "content owners" working through governments to limit use more and more. The bigger problem is that the rules of "fair use" are too variable to make general statements about them. What is allowed in EU may be forbidden in US, for example.
Personal use: fine. Beyond that, look for a license, ask, or beware.