Is the anime different from the manga?? Im confused
No. But the first few seasons are made with a different art style if that's what is confusing.
One of the seasons is short so they made it an ova instead (the one where they play Shiratorizawa). Make sure you didn't skip that. And the manga is ofc more ahead than the anime so if you came from the anime make sure you're reading the correct chapter.
The manga is really different from the anime, in the anime they add one character which is Rei Batsubami if im not wrong.
Yeah Rei is an original anime character. It's mostly the same though, only certain details are different