There are two common French equivalents for the restrictive only in English: ne... que and seulement. These two terms mean essentially the same thing, but the first is a negative adverb while the second is an adverb of quantity. Their negative forms, however, are a bit more complicated.
Ne... que is used much like other negative adverbs.*
Je n’ai qu’un livre.I only have one book.
Il ne voit que les films étrangers.He only sees foreign movies.
*Except that after other negative adverbs, the indefinite and partitive articles change to de, while with ne... que, the indefinite and partitive articles do not change: Je n’ai pas de livre vs Je n’ai qu’un livre.
The ne goes in its normal negative position in front of the verb. The que must be placed directly in front of the word it is qualifying. Note how the position of que can change the meaning:
Je n’ai lu que deux pages.I only read two pages.
Je n’ai lu deux pages que pour te faire plaisir.I read two pages only to please you.
The only reason I read two pages was to please you.
Il ne veut que travailler à la banque.He only wants to work at the bank (not invest there).
Il ne veut travailler qu’à la banque.He wants to work only at the bank (not at the store).