What I'm going to say is not exactly accurate, but in the absence of a better analogy will be this.

Bitcoin would be like gold and Ethereum like silver.

Bitcoin is now being used more as a form of ballast or reserve of other currencies than a currency itself. The other altcoins are that they are being used as coins because of their speed in transactions.

I'll give you an example of an altcoin and blockchain application.
Musicoin.
Musicoin can be used as a platform like Apple Music, Google Play Music, Deezer, Spootify, Pandora and Youtube. The difference is that by being decentralized the artist can make a lot more money by launching their songs on the platform.
Example:
Musicoin $ 0.02
Apple Music $ 0.0073
Google Play Music $ 0.0068

And so it goes. Without the intermediary the value of the product is cheaper and the artist earns more.