I've been to Huangshan twice - once to the actual mountain and once to the general vicinity.
For the mountain itself, there's now a high speed rail line to Huangshan North station opened last year, though if you're going from Nanjing then just take the K train. I went before the HSR opened so took train K645 (overnight) to Huangshan station (which is not actually that close to Huangshan!). From there you have to take a bus (or taxi) to Tangkou, which is where the entrance to the 'scenic area is' (takes maybe 30 mins by bus). When you get to the scenic area, you need to buy an entrance ticket to the scenic area and a ticket for the bus to wherever you want to go on the mountain. There are a couple of cable cars (likely to be busy) plus walking routes. I arrived at Huangshan at 10am or something so walked up the West Steps (12k) that day, stayed at the top, then walked down the East Steps (7k) the following day. All the hotels are shit, I stayed at one in the Beihai area at the summit. The weather at the top is notoriously awful, it rained a lot when I was there, no sunset as it was just a huge cloud. Got up at 4am for the sunrise, which was PHENOMENAL. After I walked down the East Steps I got a mini bus back to the scenic area entrance and stayed in Tangkou overnight, not a lot to do there but it's very chilled and cheap and I actually quite liked it as far as random chinese towns go. The following day I got a bus back to the train station, though actually I missed the train cos I'm a moron, but that's another story. Tips: make sure your bag is waterproof, take a travel towel, have a raincoat with you, take snacks, beware of crowds, watch out for monkeys. I think I wrote a blogpost about it if you are really bored and want to read it, can find the hotel links too.
I went to the Huangshan region again this year, drove there, stayed in a homestay in a village - it's a cycling/running/hiking homestay, would totally recommend: https://www.wildhomestay.com/