Hey there AaFen, we're all of us, full of love for the new guy here. OK, so prior to creating the new "Coastline" layer (which should sit atop the Clip layer), you should have had used the Fuzzy Select tool to select the grey area of the clip layer. So when you create the new layer above the Clip layer, the next step is to fill the new Coastline layer with black. It won't really matte that you can't see the clip layer any longer, because once you fill the Coastline layer (which should still have the selection on) with black you will have your initial black and white map outline on that layer. Hope that helped.

Cheers,
-Arsheesh