My phone fell down and now the screen is dark I can't see anything or

Gloria ,check your battery by removing the back cover. Remove the battery from the phone , inspect it for damage such as swelling leaking or other obvious signs of damage . If all is well reinstall it try powering on the phone and listen for the startup chimes and the vibration that usually accompanies the start up. If all this is good and you hear it staring up then the problem is with the LCD it will need to be replaced . You can purchase new screens and on ebay or amazon or here from ifixit

Galaxy J3 (2016) Screen

This video will guide you through the process

https://www.youtube.com/watch?v=ef2Oahpa...

If you dont get the startup chimes or any indication its starting up there is more serious damage done. If this is the case then contact use again and we can help from there. It is most likely the LCD will need to be replaced. Hope this helps