According to CNN, the preparations - which are in line with an NBC report from late last year that the Mueller report would be completed by the end of February - "are the clearest indication yet that Mueller is nearly done with his almost two-year investigation." Barr has said that he wants to be as "transparent" as possible while being "consistent with the rules and the law."
According to the law, Mueller must submit a "confidential" report to the AG after the investigation ends. But the rules don't require it to be shared with Congress or the public (though, like everything involving the Mueller probe, it will almost certainly leak).
One thing that remains unclear is to what extent Mueller's findings will be shared with Congress (since the DOJ typically frowns on publicizing embarrassing or compromising information about people who haven't been charged with a crime...though that principle has apparently gone out the window over the last two years).