Not all researchers want to or are able to publish in an open access journal. You can still take part in open access, though, even if you publish in a traditional pay-to-read journal by ensuring a free copy of your article is available online.
Although most traditional publishers do require you to sign over your copyright to them, many do allow authors to post copies of their articles on their personal websites and in subject or institutional repositories. Use SHERPA/RoMEO to see what your journal's policy is. If you can't find it there, contact the Libraries for help in finding out.
Make sure to pay attention to the rules that publisher's include. Most will not allow the final version of your article to be deposited but will allow the version that was submitted or accepted. Many journals also place an embargo period, usually ranging from 6 months to several years, on when you can deposit. Another requirement might be the type of website you're allowed to post on. Some will only allow you to post your article on a not-for-profit website, which would rule out sites like ResearchGate and Academia.edu, which are owned by for-profit companies.
You'll likely notice in looking through journal policies on archiving your work that they stipulate which version of you article is allowed to be posted online. See the definitions below to help clarify which ones they mean:
Submitted manuscript - Also known as the preprint version. This is the version of your article you submitted to the journal that does not incorporate feedback and edits from peer reviewers.
Accepted manuscript - Also known as the peer-reviewed manuscript or the postprint version. This version includes all peer reviewer comments and is the final version accepted by the journal editors.
Published article - The final version of your article that not only includes edits made in response to peer reviewers but all of the formatting from the journal.