Journal articles can be read in both print form and online (electronic).
Electronic articles will often have something called a Digital Object Identifier also referred to as a DOI number. The DOI is a line of numbers, letters and symbols and helps to directly locate the document when searching.
If the electronic journal article you are referencing does not have a DOI, you will then need to use the journal's URL which is often located at the top of the document and begins with www.
You will also need to use the date that you accessed this journal article in your end reference list.
Follow this link to the Cite them Write guide on referencing Journal articles: Cite Them Right: Journal Articles