What is the best way to reach the great wall? And i should go at morning?

Mariana, do you plan to visit Badaling section? You can find bus no. 5 to the west of the Forbidden City. The bus station is Beihai Station. Take bus no. 5 from there to Deshengmen. It takes around 30 minutes. Then you can take bus no. 877 from Deshengmen to Badaling. It needs around 1 hour and 10 minutes.

I personally think you should go in early morning. If you go at 08:00, then you might get there around 10:00. Spend 2 hours on the wall and then you can get back early. The earlier you get back, the fewer visitors you meet on the bus.