How does ranked 5v5 provisionals work?

So my team and I decided to play some ranked for once since we thought we were getting pretty good and we ended up fighting people way above our rank. (In other words we got rekt)

After experiencing this weird phenomenon, we were wondering just how does ranked 5's provisional matches work. Does anyone mind informing us on how it works?

Link to match history - http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1617133881/202808437