"slider" gallery photo in "Snapshot" theme has words on it?

I have “Snapshot” currently and I’ve noticed that:
1: the “slider” gallery photos won’t change
2: the words of “the slider will display your post’s featured images , so start adding some posts”

I can’t seem to insert words or pics into this slider.

NOTE: any advice must really be dummied-down for me, I am the most simplest of novices concerning this stuff.

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