"You are slow."
Translation:Jij bent langzaam.
"langzame" is an attributive adjective, which usually end in -e. These kinds of adjectives are part of a noun phrase, for example:
"de langzame koe" = "the slow cow"
"langzaam" is either a predicative adjective or an adverb (the two are not morphologically different in Dutch, unlike in English). Predicative adjectives are connected to a noun using a linking verb such as "zijn" ("to be"), for example:
"de koe is langzaam" = "the cow is slow"
It can also be an adverb:
"de koe loopt langzaam" = "the cow is walking slowly"