Implicit details are being shown but not expressed out loud.
For example:
A girl broke into her nervous habits (which were earlier revealed in the story to see which readers and characters in the story were paying attention) when she said that she was doing just fine.
Because she did not just say that she is not fine. Basically just implying some other idea without saying it out loud, not giving too much away, too much detail. She just hints at it.
Explicit details just really open up the story, trying to get the big picture by including every detail imaginable for the part of the story. For example:
Instead of saying
"She tucked the flower in her hair and was so pretty."
you would say
"She took the flower held in her hand and tucked her silky bright brown hair behind her ear. The sun, just beaming right against her face though she did not need it there, for she was a ray of sunshine. The flower brought out who she was, each petal so very softly stroking the side of her face.
etc...
