There are two processes: hydration and gelatinization
Hydration is primarily for dry pasta
once the hydrated starches reach a certain temperature they gelatinize
"gelatinization":Starch gelatinization is a process of breaking down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. This irreversibly dissolves the starch granule in water.
" Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent. "