N-acetyl-L-carnitine is a dietary supplement which breaks down in the body to produce carnitine. L-carnitine (the active isomer of carnitine) is useful in metabolism of fatty acids. Check the animation in the related links below to understand that biochemistry of L-carnitine

They do not. Meats are high in carnitine, dairy is moderate in carnitine, and trace amount can be found in peanuts and avocados.

The carnitine shuttles help transport fatty acyl coA from the cytosol of the cell into the mitochondrial matrix. The acyl group is first transfered to a carnitine and it is catalyzed into fatty acyl-carnitine by carnitine acyltransferease I at the outer mitochondrial membrane. The fatty acyl-carnitine then moves through the intermembrane space of the mitochondria through the transporter carnitine-acylcarnitine translocase. When the acyl group reaches the matrix, it is transferred to mitochondrial CoA, it is catalyzed by carnitine acyltransferase II to reform fatty acyl CoA. The carnitine is regenerated and it moves back to the intermembrane space with the aid of the same transporter.

One has acetyl in front of it.

Carnitine is needed to transport subtrates for gluconeogensis and proprionyl CoA into mitochondria.