Where the shape comes from
A footprint: the long stroke is the sole and the short ones the toes. A foot set flat on the ground is a foot that has stopped moving, which is how the word came by its modern sense. It is the foot underneath 走, and it heads 正, 步, 此 and 武.
汉字 filed under 止
No published character on HSK Guide is filed under this radical yet. 汉字库.