If you are with a public Krankenkasse, there is a month after you quit that is part of normal coverage (=no need to pay yourself), then the Arbeitsamt covers those costs for the rest of the time and also after, while receiving ALG1. If you are a private Krankenkasse, there is a also a month "free" included after you quit, but then you ought to pay yourself, until you receive ALG1. More info here.