U.S. Copyright law gives the author of an original work, such as a scholarly article, the exclusive rights to reproduce, distribute, adapt, publicly perform, and publicly display the work.....until you sign a written agreement to transfer some or all of these rights.
This brochure from SPARC gives a concise explantion of:
SHERPA/RoMEO is a service run by SHERPA to show the copyright and open access self-archiving policies of academic journals. The database uses a colour‐coding scheme to classify publishers according to their self‐archiving policy. This shows authors whether the journal allows preprint or postprint archiving in their copyright transfer agreements. It currently holds records for over 22,000 journals
Attach an author addendum to your publishing agreement in order to specify which rights you want to retain as the author.
Here are some templates and online tools to help you generate a personalized addendum.