Academic writing
A great deal of useful information on how to write a thesis is available on the Psychology Writing Center website of the University of Washington. The Writing Studio of the Radboud University Nijmegen supports writing through 'wizards': online forms which guide you through phases in the writing process. Wizards offer help for instance on planning, text coherence, audience-oriented writing or providing feedback.
APA format
If your thesis has to be written according to the APA rules, you can do the online tutorial Basics of APA style of the APA organization itself. You will also find useful information on the Psychology Writing Center website on applying APA rules, including some examples of articles in APA style.
The APA rules demand that you add the DOI's (digital object identifiers) in your reference list. To find the DOI of an article that you cite in your thesis, you can use this DOI-search programme. Please note that you have to enter the exact title. If the search machine does not find the paper, this doesn't imply that the article has no DOI, and you should look elsewhere.
In the Master Thesis Lab you can check the official APA-Manual.