Using your institutional repository for unpublished manuscripts (or even after publication) In many scientific disciplines, preprints (manuscripts that have not yet undergone peer-review) are commonly submitted to preprint servers, where they are then publicly available. These preprints serve to stake out a claim for a particular scientific finding, to generate interest prior to publication, or to show that a project has been completed - in some fields, preprint servers are also an avenue for peer review. Whether or not you are working in a field that commonly uses preprints, you should also consider the value of using your institution's repository for cataloging and for sharing your manuscript prior to or after publication.
Before publication, you can upload your manuscript prior to submission and peer-review. After publication, most journals provide instructions for acceptable use of copyrighted articles - in some cases, you are allowed to make publicly available the submitted version or even the accepted version, as long as it is not the version published by the journal. If you hold the copyright (as in a Creative Commons license such as those used by PLOS One), you have the right to post the published version.
NOTE: ResearchGate and Academia are NOT preprint servers nor institutional repositories. You may be violating copyright if you post the published version of an article there, unless it is has a Creative Commons copyright.
Example institutional repositories:
TAMU: https://library.tamu.edu/services/scholarly_communication/deposit/index
UW: https://www.lib.washington.edu/scholpub/scholarly-publishing-services/researchworks
ASU: https://repository.asu.edu/
Harvard: https://dash.harvard.edu/