While nobody knows the details, the Bible gives plenty of information on the subject. Since fishing it all out of there is admittedly a lot of work, I recommend a book which does all that work for you.
If for some unimaginable reason you are not all that interested in the details, here's the TL;DR summary.
Heaven is the Garden of Eden Restored.
Eternity is spent on a restored Earth and completely new Universe and God will live there with us.
It is not a place of sitting on clouds wearing robes and playing harps.
There is an eternity of fun and fulfilling work to do.
Some who have done well in this life will get important jobs like, say, supervising the Sagittarius Arm of the Milky Way.
Others will run a lemonade stand in the Bronx.
But that's just the rewards for Christian believers.
An opportunity open to everyone.
You all know what happens to those who reject that generous offer.
I'll spare you the details.