Flex Que Question.

How does Flex Que actually work ? is it any rank vs any rank ? like this makes no sense I was in a game just now in BRONZE 1 PROMOS .... against a PLAT 2 RIVEN .... LIKE WUT ? HOWS THAT FAIR ?

Riot man what are you doing ? why am I being put up against a DIAMOND player in BRONZE ...

How is that possible in Flex Que should I just get some diamond to carry me to gold ? is that how flex works ?