well most of them are currencies, and you can use them for certain transactions. your purpose though is investment right now and if everyone does only that, then i don't think that they will accumulate in value because if no one is using dollars to trade, then their value will also drop because it is not following the value of money rules. most new cryptos are targeting a certain field per say but in the future, many vendors will accept them as payments.

in short, you buy a new form of currency with your fiat money, almost like dollar > pound except that the pound may not be accepted in many places.