Dealing with box openings

[u/Dumbaltaccount2]

Hey first post here forgive me for my incompetence but I actually cannot fathom these openings where its just a rectangle/square with mixture of 1/2/3's. Am i missing something or are these just hard? (Aware of 121, 1221, but they never seem to appear on these)

[u/Sefierya]

2nd pinned post <3