Actually, you should fill in that application and that's it. No other things attached because this is the purpose of an application. To select the relevant info about you for a better processing and future selection of candidates. I would definitely recommend you to make a short resuming of your job experience just for situations like this. If you have some explanations to give, use less words which say more. The job application is not a place to develop this topic either. They will ask you about your reasons for leaving a job during the interview

More suggestions regarding a job application:
http://www.careeradvicecenter.com/job-search/prepare-to-fill-job-application-form.htmlStephanie