Answers for "flex box use"

css flexbox syntax

Display: flex 
Flex-direction: row | row-reverse | column | column-reverse
align-self: flex-start | flex-end | center | baseline | stretch
justify-content: start |  center | space-between | space-around | space-evenly

flexbox

Please read flexbox & grid in CSS TRIX, 
make hands-on project watching (WESBOS videos - it's really useful)
also try [FLEXBOX - froggy] and [GRID - garden] games

flexbox in css

flex-box by order
.item {
  order: 5; /* default is 0 */
}