Its an oversimplified explanation. The blockchain forms a Merkle chain of unalterable history, whereby correct knowledge of the present can be used to verify correct knowledge of the past. Adding a Hashcash-style POW function for transaction ordering, it becomes a Byzantine fault-tolerant distributed database with no central authority or trusted supernodes. Thats the simplest explanation I can provide in two sentences.
All very fine but it won't scale as implemented by Bitcoin and hashing of hashes, well the credit has to go back to Bit-Torrent
for that one and I am yet to see anyone using a block-ledger (My invention) but i am sure someone will cotton on or were using
it long before I thought it up.
The solution to making the block-chain scale has been going off-block and we certainly have "supernodes" on that
as can be seen here
https://lnmainnet.gaben.win/