Hello everybody!
Okay, now I think I know what the problem is (that's me, hah haa).
I tried to open the library from Sketch > Import Library > ... and that's what I did wrong. The right is just open it from File > Examples > ...
I did like this (and this is wrong):
I should do like this, and this works:
Thank you all for your support!
Be ready, I have soon some more questions XD