Research papers are written in a format and a style that is a bit different from your textbook, and from the newspaper and magazine articles that you've read so far. They can be a bit overwhelming to read the first time you try to read one, and even the second and hundredth time.  Here are some suggestions to make the process a bit more manageable:

Read with a pencil!  Make a copy of the article, so you can scribble notes on it and underline things you'll want to return to.  Look up important words that are unfamiliar to you in a regular dictionary, such as the Dictionary.com site or a specialized dictionary like the On-line Medical Dictionary.  

Research papers are written in a standard format, which makes it easy for the experienced reader to know just where to find certain kinds of information:  the background here, the details of the methods there, etc.  However, you don't have to read the article in the order in which it appears.  

2. Read the introduction.  This is where you'll find the background, where the authors mention what is known about the field now, and what they see as the justification for doing the research that they've done.  They usually start with a very general picture of the field, then zoom in on the particular particular problem that they will address here.  Sometimes the authors actually give one sentence summarizing the results right here, so that the reader has a sense of why the study is important.  

3. Once you understand the basic purpose of the experiment from the Introduction, try to get an idea of the design of the experiment.  You can find this by skimming the Abstract or the Materials & Methods (This section is supposed to have enough information for another scientist to repeat the experiment, so it's more detailed than you need right now.)  Make a flowchart of the experiment as I did in the Experimental Design slides, to clarify in your mind exactly how they did the experiment.  

4.  You can jump to the Figures and Tables which will often be the best summary of the actual results.  Read the legend and summarize what the results seem to say.  Considering the purpose of the experiment, what do you think of the results?  How would you interpret them?  Do you think they support the authors' hypothesis?

5. Read the Discussion.  This is the place where the authors discuss what they think of their results, so make notes of their critique of their own work.  What do they see as its limitations?  What do they think the next experiment should be? How do they think it relates to what's already known in the field?

6. Go back to the Abstract, and read it carefully.  This is what the authors consider the most important message of their paper, and now you should understand it too.

7. Look at the Materials and Methods more carefully.  Why did the authors do the experiment in this way?  Is there another way they might have done it?