The Fantasy in D-Minor by Mozart was one of Mozart’s pieces that was discovered after his death (since it was unfinished, it wasn’t published in his lifetime).
The 1782 date of composition is an estimation based on its style in relation to other Mozart works (he was really into writing and learning Baroque music at the time).
As for the musical style, Fantasias are improvisation-style compositions. They’re very free-form, and don’t conform to specific writing structures (like, say, a minuet or a sonata). Sometimes they serve as introductory material, paired with a fugue (Bach in particular wrote these, and so did Mozart).
Many pianists have performed their own versions of this piece. We have two for you today; chose which interpretation you prefer:
Here is Mitsuko Uchida’s version:
And here is Emil Gilels Playing the same composition:
