If you're interested in a particular journal or magazine, and want to find the Library database where it's located, use the Publication Finder. This online tool allows you to search by title or subject, and will show you which database contains full-text coverage of each periodical.
For example, if you search for the magazine title Health Care Biller, the directory will show you that this magazine is available in the Associates Programs Source module of the EBSCOhost database, and the full text of articles is available from 1999 to the present.