Which is the best point at Great Wall and how I could reach there.

There are several sections of great wall located in Beijing, such as the Badaling, Mutianyu.
Badaling is most typical and best-preserved one, while personally speaking, Mutianyu is more majestic.
The best point must be the top point of the wall, where you can have a bird-eye view of the lowland, which makes you fees refreshed. There are cable cars up the wall, you can take that.