Twenty Fourteen Featured Content Problem, Need Help !!

Hi , Am using WordPress on Bluehost.com with the twenty fourteen Theme which i found the best for me .
the problem is that i cant get any posts to appear as a grid or slider , now I’ve seen much posts about this problem all over the internet but nothing seems to be working for me , I’ve changed the tags name many times , disabled jetpack and enabled it , changed posts , I’ve literally tried everything but nothing worked .
am all new to all of this but nothing that i couldn’t fix until this problem came up , now when i tag the post to make it appear in grid or slider , the post disappear from the page like it not even there !!
so i appreciates any help here .. thank you !!