First, you can enter heaven while alive and not die, it takes the same effort either way. Shortly after death Archangel Azrael 'the grim reaper' offers her assistance, if you decline she will come back in a week and offer again, if you decline again then you be left to find your way back on your own, which may take awhile so I strongly suggest accepting her help. You basically exist in the astral plane which could be all kinds of places. Interestingly religious people, since they believe in a stero typical heaven so strongly, it actually exists, the white clouds and all that stuff, its fabricated but they think its real and get stuck there for awhile but eventually realize its not because things that arn't eternal can't exist for eternity.

Beyond that, you return to eternal reality entirely, language is too basic.. or possibly too complex to describe that, experience only.