Beside what one gets in that intro text and the MC's dialogues with Riddle, not much really.
Voldy was apparently more spiritually unstable than book version, resulting in a somewhat larger fragment of him ending within Harry, what would lead to a merge of sorts and corruption of the child from the get-go. Turns friends with Malfoy instead of Weasley, when he comes across Voldy-shade within Quirell in this verse's version of Philosopher's Stone, "Dirty Harry" just absorbs him, becoming Voldemort Redux fully.
Some still unexplained events happen along the way that result in the Diary somehow ending hidden within Hogwarts (where the MC finds - or more precisely is found by - it) instead of in Lucius' hands.
The diary is not only sapient, but implies Riddle is mostly aware of what is going on with Voldy & Harry
and wants that shit very much away from it, ergo why he's in an alliance with the MC to increase his power and eventually defeat Potter (that dislikes the MC and regularly bullies him through other students, for reasons).
There's also some explanation of why Riddle is (supposedly, the diary could be lying about his real motives to exploit the MC)
not the ruthless maniac we might expect and why & how his other self would diverge and evolve into Voldemort as we know. It even ties up into the dementor-like trick the MC uses to speed run his magical growth. That said, "empowerment through horniness" was wholy the MC's idea and the diary itself thought him an idiot genius for finding a solution to the one danger of the technique, so to speak.
But yeah, so far all the MC does is enchant people to make them hornier, feeds on lust to increase his magical reserves & skills, while exploring Hogwarts and avoiding attracting the attention of Harry's clique and other more influential students. Also, the more the MC focuses in a house the higher the general debauchery goes, so much so
the teachers themselves may become degenerates before you are powerful enough to corrupt them. as i found out when i finally got strong enough to tackle Sprout - only find her already banging a student and be offered to join in a threesome.
MC may also, depending on player's actions, end up saving
a lot of girls from magical botches by stupid colleagues or rape attempts by groups of abusive senior students, what could be used by the Dev as a hook for him to get some allies in the future. Also guessing from the list of character bios that many classic characters plus the MC's roomates will get more participation in the future.