You can burn wood pellets in a regular fireplace but to burn wood pellets in a fireplace you need a pellet tray or insert to put into your fireplace to burn the wood pellets.
In a traditional fireplace the wood pellets won't put out much heat but it's good for the look of the fire and does produce at least some heat.
If you want to burn wood pellets as a heat source then I recommend getting a pellet burning stove to heat the house up efficiently and get the most heat out of the wood pellets.