How do reports and warnings work

Hi all! I want to know how do reports and warnings work; I haven't played for 3 days and today i played one classic and one ARAM. After the ARAM received a warning that i was reported for negative attitude. So i want to know if that warning was just from a single report of the last 2 games i played today, or the warning was sent after more of reports summed up during a longer period. And also are warnings sent/approved by staff? Are reports reviewed by staff? (If staff is reviewing reports) For which categories of reports Is chat reviewed by staff? The reason Im asking this is because i was confused; in the both games i wrote only "shut up" in the first one to an enemy (he/she was spamming). So I want to know if it is a sum form my previous behavior(don't remember much of that) or was some one trolling.
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