Put on gardening gloves. Cut open the hay bale with scissors or a sharp knife.
Start in the back corner of your seeded area facing the corner. Prepare to spread the hay in front of you, walking backward as you spread. Walking over the hay can displace it, so spread it in such a way that you don't step on the newly laid mulch.
Spread the hay by hand over the newly seeded area. Break up clumps so the hay provides even coverage. You should be able to see some dirt through the hay, which should cover about 70 percent of the ground. In warmer weather, you only need about 50 percent coverage, but more mulch helps the soil hold heat during the colder months.
Water the seeded area thoroughly when finished covering it with hay. Water the area daily for the first two weeks, or until you see tiny blades of grass beginning to poke through the soil.
Leave the straw on the ground as the grass grows. It will break down slowly during the winter, adding essential nutrients to the soil to help keep the grass healthy.