。
Please feel free to use it.
Literal
Honorable-hesitation-without honorific-use [please-ください].
ご遠慮なく is a set polite phrase meaning 'without holding back,' composed of the honorific ご + 遠慮 'reserve/hesitation' + なく (the adverbial negative of ある). お使いください follows the respectful request pattern お+[verb stem]+ください. The whole phrase is a stock hospitality formula — short, formulaic, and extremely common in service contexts.