how do we travel from hangzhou to tunxi then tangkou in order to go Mt Huang Shan?

To reach that mountain, there are two method. The first one is to take the bus from Hangzhou West Bus Station to reach Tunxi. Upon reaching Tunxi, you can find the direct buses to reach Tangkou directly.
The other method is to take the direct the mountain directly.

How much does it cost to take the bus from Hangzhou? And where will the bus drop us in Tunxi? Is it the drop off point to take the bus from Tunxi to TangKou?
What is the other method? U have only mentioned "to take the direct the mountain directly"? Don't get your point.

The bus fare from Hangzhou West Station to Tunxi is CNY88 per person. It will take you to Tunxi Bus Station in HS city, where you can take a bus to Tangkou.

Apart from the way above, there are direct buses between Hangzhou West Bus Station to Tangkou, HS scenic area. The bus fare is CNY98-110.