I am not quite sure what you’re asking about but note that the line you have marked on the tip block refers to hollowing that block.
It roughly indicates the ‘pocket’ you’re supposed to carve out of that block.
To avoid frustration further on, the way I would do it is tack glue the tip block, carve and rough sand the outer surface to shape, then remove it from the wing and carefully hollow out leaving enough thickness so the tip doesn’t become too flimsy.
It’s a trial and error process, work slowly.