There are thousands of different kinds of mold, some are toxic, some are not. Some are even necessary to make food nice: camembert, blue vein cheeses, soy sauce and some desert wines get their flavours fom certain molds grown in controlled conditions.
If you find a moldy item in your fridge, it is impossible to know whether the mold is harmful or not, so it's best to avoid it.
If you've eaten some and are having trouble breathing or are feeling ill, go see a doctor.
I would never eat mouldy meat, but I know I've had (small amounts, generally accidentally) moldy bread, cheese or jam and had no side effects (as far as I know).
As far as I know salmonella bacteria re not classified as 'mold'.