Short answers, pulled from the story.
The Homeric Hymns are a collection of thirty-three ancient Greek hymns and one epigram. Most date to the seventh and sixth centuries BCE, though the latest, the Hymn to Ares, may have been composed as late as the fifth century CE.
Irene de Jong has contrasted the narrative focus of the Homeric Hymns with that of the Homeric epics by noting that gods are the primary focus of the hymns while mortals serve primarily to witness the gods' actions. The poems make use of iterative narration within passages of singulative narration which is relatively rare in ancient Greek literature.
The Hymn to Demeter covers the abduction of Persephone and Demeter's attempt to recover her from the Underworld. It details the origin of the cult of Demeter at Eleusis.
Percy Bysshe Shelley made a translation of some of the shorter Homeric Hymns into heroic couplets in January 1818. Leigh Hunt published a translation of the second Hymn to Dionysus in 1814 and Thomas Love Peacock adapted part of the same hymn in his Rhododaphne published posthumously in 1818.
Both the first Hymn to Dionysus and the Hymn to Demeter were lost until 1777 when Christian Frederick Matthaei discovered them in a barn outside Moscow. The rediscovery of the Hymn to Demeter in 1777 sparked a series of scholarly editions of the poem in Germany.