You can also check the Instructions for Authors on the journal's online site to see what the publisher's default copyright arrangements are. Search Google using the name of the journal in quotes to find the publisher site.

If the journal doesn't post its copyright requirements for authors, send a letter inquiring about/requesting self-archiving rights. Contact information for publishers can be found either from the Instructions for Authors or via the Copyright Clearance Center http://www.copyright.com/
 

Before signing the copyright agreement with your journal publisher, check to see whether you retain the right to self-archive a copy of the article on a website of your choice, and whether the right is to a preprint or postprint copy.

You have the right to negotiate with your publisher to request those rights.

The Scholar's Addendum Engine helps you generate addenda to add to your copyright release specifying self-archive and/or open access rights: http://scholars.sciencecommons.org/

Some but not all government grants urge or require the Open Access availability of publications based on those grants within a time after publication. MIT has a useful list https://libraries.mit.edu/scholarly/research-funders/  but it's not exhaustive. 
If your grant requires open access availability, you'll want to check with your funder whether they have rules about when & where the publication should be posted. Obviously, you'll need to disclose such obligations to your publisher before signing anything.