Well they use corn starch commonly in liquid like foods like soups, etc... They mix corn starch with the cool temperature of the liquid to form a paste like substance. It is sometimes preferred over flour alone because it forms a translucent mixture, rather than an opaque one. As the starch is heated, the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid.
I hope this helps. I suck at baking haha.
