Where the shape comes from
A head shown with hair or a crest marked along the top, the topmost, leading part of the body giving the word its extended sense of first, foremost, chief. It names the leading city in 首都, a capital, and the leading person in 元首, a head of state, and opens a list or an account in 首先, first of all, to begin with.
汉字 filed under 首
No published character on HSK Guide is filed under this radical yet. 汉字库.