New to sewing…Please help Sewing Machines Parts and Sales in Los Angeles

I was wanting to make a sweatshirt for my honey using the pattern McCall’s M6614, the option D for those who know the pattern. I was going to buy my fabric from SpoonFlower because of a specific design, but I do not know the correct or best suited fabric to use. If I could get any suggestions that would be wonderful. I know that from my pattern they suggest a moderate stretch knit fabric, but I am unsure as to what that would actually mean. Thanks to everyone in advance.