Tangkou is the main point of access for Huangshan and the only one to the south of the scenic area. It has all the facilities expected of a tourist town.
Your hotel will likely be able to book bus tickets but these may not be National Express services. Instead they may offer slower, less comfortable buses that pick up from the hotel. They are a reasonable alternative to the National Express buses.
If all else fails you can get a National Express bus by taking a taxi to the western part of Tankou's city. There, near to the freeway station, is the long distance bus station. Bus ticket price back to Shanghai was in april 2012 ¥140. Back to Hangzhou ¥100. An online timetable for services from Tangkou can be found here 
The other common way of getting to Tangkou is via Tunxi which has good transport connections including bus, train and plane. From Tunxi you need to take a bus to Tangkou 汤口 (aka Mount Huangshan Scenic Area 黄山风景区). The buses are found 20 meters in front of the main station entrance and they leave every 10-15 minutes. It should cost 20Yuan and take 1 hour. Pay on the bus.
If you want to travel directly from Hongcun to Tangkou (about 45 minutes) you need to get a private driver. Those drivers wait in front of Hongcuns main entrance gate. One ride is 100 Y (May 2014). You can ask the driver to look for more people going there, to save money. You will most probably want to go to Tangkou's city centre and might want to clarify this in advance. The drive itself is quite scenic and the road seems to be rather new. The drivers like to go fast though, so buckle up!
Tangkou is small enough to be walked. However many hotels have minibuses and will take you to the bus station or other common destinations. There is a river that has several restaurants, super markets, a bakery and fruit shops on both sides. Good for getting everything you need for the trip to Huangshan.
There are no attractions in Tangkou. Try to arrive in the late afternoon or evening. Shops and restaurants are open until 10 pm or 0 am. After dinner and preparing your trip to Huangshan, there's nothing left to do in Tangkou.
See Get Out
English language maps of Huangshan are available but may be outdated.
There are many restaurants. Most serve local cuisine including for example Chao3san1xian1 (fried bamboo shoots, Mu'er and Shiitake/Xianggu). If you visit the region in spring, you might want to try a dish with bamboo, which is in season during this time. Next to the river running through town is a surprisingly good bakery (just opposite the largest super market). A very nice local restaurant called Haozailai (好再来菜馆）is located on Yanxi (meaning riverside) West Street, where you can find super authentic and delicious local cuisine.
In Tangkou there are a lot of cheap hotels available for around ¥80.
The main thing to do in Tangkou is to head to Huangshan. You cannot go direct to the mountain entrance by taxi: only the National Express shuttle buses are allowed into the scenic area. You can walk, but it is not recommended. Shuttle buses are available to either Mercy Light Temple for the Yuping (aka Jade Screen) Cable Car or to Yungu (aka Cloud Valley) Cable Car. They leave from the town approximately every 20 minutes, cost ¥19 and take around 20 minutes.
Getting to the long-distance bus station (e.g. if you want to go to Shanghai) is a bit tricky, since there are no taxis. There are however nice ladies around the main road (just ask around if you don't see them) who will then call a driver. It's about 10 minutes and costs about 20-25 Y per ride (May 2014).