、。
If you need books, make maximum use of the library's books.
Literal
Books [subject-が] necessary [if-なら], library [attributive-の] books [object-を] to-the-maximum use-[gentle-imperative-なさい].
The なら conditional is used for 'if (given the topic/supposition) X.' Distinct from たら (temporal/sequential 'if/when') and ば (general conditional). 最大限 ('to the maximum extent') is a Sino-Japanese noun functioning as an adverb. 利用する ('to use, utilize') is formal compared to 使う.