Summarize this article in one sentence.
Mushroom kits normally have all of the materials that you need for planting and growing mushrooms, and are great for beginners. They usually contain manure, substrate, trays, and a spray bottle for watering the mushrooms.  Growing kits tend to have specific directions that may differ from traditional mushroom growing methods. Be sure to read the package carefully and follow the directions. Some kits already contain the spores for growing a specific type of mushrooms, while others just contain growing trays and appropriate substrate. Select trays that are about 14 by 16 inches (36 by 41 cm) and at least 6 inches (15 cm) deep. To start out, only plant in one tray, which will continue to produce mushrooms for 3-6 months.  Trays can be made of plastic, metal, or wood, depending on what you have available. As you become a more experienced cultivator, you can grow multiple trays at once and have an almost constant supply of mushrooms! Button mushrooms require a growing environment that contains a lot of nitrogen. Use your own compost and purchase manure, like horse or cow manure, at the store, or buy both if you don't have a compost pile.  If you plan on growing a lot of mushrooms, you can make this mixture in a large bucket and cover it after you use some of it. Otherwise, only mix as much as you'll need to fill one tray. Your manure and compost mixture will produce a strong smell, so make it in a well-ventilated area. Pour the mixture into the trays carefully, leaving at least 1 inch (2.5 cm) of space at the top of the tray. Make sure the soil is level and is spread evenly across the tray. White button mushrooms tend to spawn well in warm compost, so don't worry if the compost is still hot when you place it in the tray.

Summary:
Consider buying a kit if it's your first time growing mushrooms. Buy large trays for growing the mushrooms. Make a mixture of equal parts compost and manure. Fill the trays with 6 in (15 cm) of the growing mix.