You just need to submit your original manuscript as a single PDF file to be used in the refereeing process. No specific format is required at this stage, but we suggest that the general article structure and templates are used. Only when your paper is at the revision stage will you be requested to put your paper in a 'correct format' for acceptance and provide the items required for the publication of your article. You can find the general article structure here.
If you are using Latex, then could you please use the article class elsarticle.cls to prepare your manuscript. For detailed submission instructions, templates and other information on LaTeX, see http://www.elsevier.com/latex