When you write a paper, you automatically own the copyright to your work unless and until you explicitly transfer your copyright to another party through a written agreement. Your copyright is really a bundle of rights that includes exclusive rights to your work, including:
When your article is reviewed and accepted for publication in a journal, you will be asked to sign an agreement to allow the journal to publish your work. Many journals use copyright transfer agreements as their standard publication agreement. If you sign a copyright transfer agreement with a publisher, you transfer your copyright to the publisher. Unless the agreement includes provisions allowing you to retain some of your rights, you may no longer have the right to place your work on websites or researcher profile pages (e.g. ResearchGate, Academia.edu), use your work in teaching your courses, reuse the work in subsequent works, or deposit the work in an online digital archive.
When you publish your paper, it's important to think about the rights you wish to retain. Transferring your copyright does not have to be an all or nothing affair, and some publishers are willing to negotiate which rights are transferred and which you may retain.
There are three different types of Open Access: