。
I'd like to make a dinner reservation for tomorrow night.
Literal
Tomorrow [possessive-の] night [possessive-の] dinner [possessive-の] reservation [object-を] please.
A textbook polite service-industry request. をお願いします is the standard way to request something from a service provider — literally 'I ask for X,' not 'I want X.' Notice the stacked の particles (夜のディナーの予約) building a noun phrase piece by piece; each の marks the preceding noun as a modifier of the next. Subject is omitted — the speaker is obvious from context.