If it is available online, there will be an internet link in the bibliographic record that you can simply click on. Some publishers also make articles freely available after a certain time period, like 6 months or a year. Others have unlimited access for an introductory period in order to get people to subscribe. An example is Developmental Biology. Access to it is free this year.
Electronic access is clearly the wave of the future.
A number of influential people are trying to make electronic access free for everyone. The publishers don t like that idea because they will then have to get money from the authors and authors would balk at paying fees that would maintain the profit margin of many publishers. A new independent enterprise encouraged by the NIH called BioMed Central just started publishing articles this year. The papers undergo the same kind of peer review as other journals but they are only published electronically. The articles are published almost immediately upon acceptance, Medline indexes their abstracts, the author keeps the copyright to the paper and anyone can get pdf copies for free from their web site.