WHOLE CHARACTER
坐zuò
to sit; to travel by (坐车, 坐船); to be situated (坐北朝南)
坐 is to sit — two people at rest on the earth, and to travel riding.
The header pictures two people seated on the earth; in the modern form the strokes overlap, shown as the paired-person group over the earth base.
PAIRED-PERSON TOP GROUP (人人)
从cóng
to follow
A standalone character; used in 坐 to show the paired-person group, whose strokes overlap the base in the modern form.
In 坐: paired-person top group (人人) Two person forms side by side, written here like the character 从; the strokes overlap the base in the modern form.
EARTH BASE (THE RADICAL 土)
土tǔ
earth; soil
Repeated in 垚.
In 坐: earth base (the radical 土) ZDIC lists 土 as the radical.