"Attributive adjectives" are before the noun (the fat man)
"Predicative adjectives" are after the noun (the man is fat)
Of course, predicatives need a verb before the adjective (you can never say "the man fat")
Also there are a few adjectives that can only be used predicatively, like "alone"
The alone child (wrong)
The child is alone (OK)
...and a few that can only be used attributively, like "main"
The main reason (OK)
The reason is main (wrong)
Most adjectives can be used in either position, though, so don't worry too much about it. Hope this helps.