Adding fertilizer to your lawn at the right time with the right mixture can keep your lawn growing, healthy, and looking great. It is important to know based on your climate when is the best time to fertilize, although spring and fall are good general rules of thumb. Make sure not to fertilize too much, as this can cause your lawn to burn creating a really poor appearance and a possibility of having to replace it.
Your two main components with this gardening task is to have a fertilizer spreader and the actual fertilizer you want to use. There are rolling spreaders as well as handheld spreaders, and you might want to get one that is appropriate for the size of your lawn.
Read the directions from the fertilizer and adjust the settings on the spreader to match. Here is a quick video from MonkeySee and the National Gardening Association.