For block rewards you'd have to mine. In particular you'd have to have a server running a node joined in the network ready to generate a block whenever your number is called.
Not everyone would want to do that, so there's usually a mechanism to indicate you want to be eligible to do so, depositing your coins or similar.
That's for block rewards - nothing prevents a blockchain currency to be designed to generate inflation and add interest on everyone's investment - some do exactly that.
