When you throw a rod in an engine it means that basically the rod that connects to the crankshaft and piston has broken off or is about to completely break off.
When the piston rod actually breaks and throws it will slap around in the engine and damage the crankshaft and can potentially even throw the rod through the engine oil pan.
I've had that happen before when I was driving and the engine threw the rod and it literally threw the rod through the engine oil pan and leaked the oil out.
If you throw a rod through a steel engine then it might be able to be fixed with a complete engine rebuild which you can do yourself for around $500.00 if you know how to rebuild the engine.
But if you need to pay someone to rebuild the engine for you then you might be better off either getting a new or used engine or getting another car.
If the engine is an aluminum engine block then throwing a rod could damage the engine block which then it may not be able to be rebuilt.
If you hear a constant knocking sound from your engine you should stop driving it because you could spin a rod bearing which could then lead to crankshaft damage and even possible throwing a piston rod.
A piston rod being thrown in your engine requires extensive repair.