A template is a model or a guide for producing something. When you build your website, you might use a free template, filling in your own text and images.
Template has a few different meanings, but the most common one is as a pattern that can be used in building or reproducing something. If you are designing costumes for a production of Shakespeare, you might use the design of one of Queen Elizabeth's dresses as a template to work from. In building, a template is a block of wood that goes under a door or a wall to distribute weight.