The Flex-Direction CSS property sets how flex items are placed in the flex container defining the main axis and the direction (normal or reversed).
The flex-grow CSS property sets the flex grow factor of a flex item's main size. It is property is specified as single number
The flex-basis CSS property sets the initial main size of a flex item. It sets the size of the content box unless otherwise set with box-sizing.
In this reference document it talks about how the flex is done using different kind flex layouts including flex-direction, flex-grow, and flex-basis.