When publishing an article in a journal or book, authors often sign a copyright transfer agreement or similar document (e.g. licence to publish), in which they transfer to the publisher the right to publish their work, and the general terms and conditions of the publisher apply.
Some rights remain with the authors, but these are broad or limited, depending on the publisher and the journal. In the past years many publishers have decided to allow their authors to self-archive their articles with open access in an institutional repository such as ZORA - mostly they allow the accepted manuscript (author's post-print), while the published version (published PDF; publisher's version) is handled more restrictively. Sometimes these files may only become publicly accessible after an embargo period of 2-24 months.
Difference between an accepted manuscript and a published PDF: Information
Use the database Sherpa/RoMEO to find a summary of permissions that are normally given as part of each publisher's copyright transfer agreement. The database also offers links to original licences and answers how to self-archive publications.
Specific rights of self-archiving in ZORA are listed in the Journal Database hosted by the ZORA editorial office.