It’s a vitamin like compound responsible for the transport of long chain Fatty acids into the energy producing cell units i.e. the mitochondria
Carnitine is essential because it is critical in the transport of fatty acids into mitochondria. Since the carrier molecules of fatty acids, acyl CoA can’t penetrate the cell membrane of the mitochondria results in reduced energy production.
The fatty acids must be transferred from CoA to carnitine. The acyl carnitine molecule can then transport the fatty acid molecule to the mitochondrial surface of the inner mitochondrial membrane. There it releases the fatty acid, so that it can be converted to energy.