After recording some videos, I took the camera out of drone set it on a reader and plug it to the computer, I see the files but they do not play. Will anybody explain how to dowload the files
Do you mean the SD card? The Camera is not removable.
Here is the User Manual and on page 9 you will find the instructions for installing and removing the SD card.
Depending on the settings you make for the camera in the YuneecPilot app photos will be in JPG or DNG file format and videos will be MOV files. Assuming you have a Windows computer use File Explorer to navigate to the external drive created when the SD card was inserted. Double clicking a JPG photo or MOV video should open it for viewing.