For text, the Origin sets the point a text element stays anchored to as its content changes length. You set it in the Position & Size section of the Property Panel, using a grid of nine points: the corners, the edge midpoints, and the centre.
A text box resizes to fit its content, so when the text gets longer or shorter the box grows or shrinks with it. With a centred Origin the text expands evenly to both sides; with a bottom-left Origin the bottom-left corner stays fixed and the text grows up and to the right.
This matters most for text that comes from a text input field: your users type headlines and labels of every length, and the Origin keeps the text anchored the same way no matter how much they write.
The horizontal Origin and the Align setting in the Text section mirror each other: a left, centre, or right Origin is the same as left, centre, or right alignment, so changing one moves the other.