What is Dc New Universe?

So it appears DC is rebooting the universe does that mean their starting from scratch because it my mind it seems that all of the characters existing now will change like some wont exist at all example what about roy harper all they put him through and now whats going to happen to him with green arrow now coming back to normal hero status is he even going to exist and what about batman Incorporated looks like robin will have to start over .it seems like all the history and things they are doing have just gone up it smoke is this what they are doing or just changing these characters and keeping others the same.it just makes me feel weird that everything being left