The amount of time that it's safe to leave food out is for 2 hours.
If you leave the food out longer than 2 hours then it can grow bacteria pretty rapidly especially when the room temperature is pretty hot.
The hotter the room that the food is left out in the faster the food will grow bacteria and spoil.
For most foods such as foods with meats that you left out longer than 2 hours it should really be thrown out because it can cause food poisoning if bacteria has grown in it.
Some other foods such as noodles etc might be safe longer than a couple hours but if it smells bad then throw it out.
Any foods that you want to keep longer than a couple hours you should either freeze the food or refrigerate it.
If you're gonna eat the food within a few days then refrigerating the food is fine but when you freeze the food it will last 6 months to a year.
The freezer keeps the bacteria from growing on the food.