Before saying what is Developer Portal let's play a game.
Imagine your home. Inside your home you have people and usually more stuff than you need but that exist for some reason. Everything has a status (even if it is a broken one...), a place to be (unless you have kids), and some form of interaction with the ones who live there or visit respecting some sort of rules and order.
Now imagine you have a tool wich gives you imediate access to a list of all the stuff you own and its status, purpose and instructions of use.
Developer Portal wants to be that tool to our developers community, giving acess to the most meaningful information about what really matters to them.