If the articles you want your students to read for class are available through the library, it’s best to post the link to the article on Blackboard, rather than uploading the PDF. This helps the library keep track of what sources are actually being used (which helps us decide what to buy in the future), but it is also the appropriate way to use copyrighted sources ethically. For more information on linking to resources on Blackboard, see here.
When an article is unavailable through the library, you will likely need to purchase it. There are some limits on what you can do with an article you purchased as an individual, but it’s ok to use printed copies of legally purchased articles in a face-to-face class. This would be a fair use of the item—a one-time, restricted-access use for educational purposes. For more information on fair use, see here.