The best way I always explain it is like so:

If you need to transfer something to someone, you have a record and they have a record of that transaction. In Blockchain, there is only 1 central record that can not be changed.

This is simple, but if you add 10+ companies to the mix as they trade, exchange, build, consume all of these records can get messed up very quickly. With one central record 'database' the world can be a much simpler place.