I’m not sure how deep you want to get, but have you considered the Book of Concord? It’s a compilation of the original Lutheran Confessions, penned by the original Lutherans in the mid-1500’s (Luther, Melancthon, etc.). That’s really the only place you’re going to find the full answer to “official” Lutheran beliefs.
From a Roman Catholic perspective it may be quite helpful, because the Confessions were written directly addressing what they believed were the errors in Rome’s doctrine. But they will also show many points where honest Lutherans and Roman Catholics share commonality.
For example, both firmly believe the Real Presence. Lutherans do not fix a point in time at which it happens, where Rome does. Lutherans believe that the one and only Sacrafice has already been made and that the Mass is not a “sacrafice.” Yet Lutherans share much of the same liturgy with Rome.
Unless you go back to the original Confessions, you are likely to get any range of answers from current day Lutherans. Some Lutheran denominations say they hold dearly to the Confessions, yet they turn around and enter into official fellowship with protestant denominations that hold beliefs directly contradictory to the Lutheran Confessions (such as denying the Real Presence). It’s a sad condition. Some like being called Lutheran and want to hold on to the name, yet they don’t want to maintain the beliefs.