Congratulations on your new purchase! Antivirus software is very important to have, and there are several free options available online. This article from PC magazine outlines the best free antivirus software in 2015, and gives you an infographic that represents the different features available with each product.
Here is the link to the article: http://www.pcmag.com/article2/0,2817,2388652,00.asp
I would suggest that you review the different products that are listed in the article to see what would work best for your needs. It appears that AVG, the first product listed in the infographic, might be the best, but there may be a different product that you prefer more. To download the software, you should be able to access it by clicking on the title of the product and following the links to the specific site.