hello! first of all: that tutorial is two years old so i apologize for eventual mistakes or badly explained points, i really should go and fix a few things but i’m very busy with life so.
anyway. presuming that you only deleted frames that were at the beginning and at the end of the gif, leaving the middle ones untouched, you only need to see which layer matches with the first frame and which one matches with the last frame. the middles frames will correspond to all those layers between the first layer and the last one. if you see the little eye next to the layer (i’m referring to the layer visibility symbol) it means that, on your frames window, the corresponding frame is selected.
for example: you’re on your first frame
but on your layers window, that frame’s corresponding layer is actually the second layer, and not the first one. so the first layer is absolutely useless since it won’t appear in the actual gif (because you deleted its frame)
you only have to delete that “layer 1” because you don’t need it, seeing as your gif basically starts from “layer 2”. the same thing could happen at the end of the gif or even in the middle if you deleted frames from the middle of the gif. it’s all a matter of visibility of the layers, if a layer is never visible whatever frame you’re selecting, then it means that that layer isn’t in the gif at all because you deleted its frame.
i hope this cleared things up a bit? it really isn’t difficult. i don’t even know if i actually read this somewhere when i learned how to make gifs or if it’s something i got around doing myself but i think it’s pretty useful because it makes things much tidier. anyway it’s not necessary, you could go ahead and forget about this passage and your gif would look the same so don’t worry about it if you still don’t understand (i hope you do though?? if you don’t it means i’m really bad at explaining stuff lol)