Ng is a very useful word in the Filipino language. It can be directly translated to the word of in English. For example buhay ng tao which means the life of a person. One can also say dulo ng landas which means end of the trail or ihip ng hangin which means blowing of the wind. You might as a poet say bakas ng kahapon which means footprints of yesterday or indayog ng mga alon which means rhythm of the waves.
But there's another function that ng performs in the Tagalog language which is its use as a helping word to make the phrases easier to say and make the sound smoother to the ear. We have to thank the Filipino forefathers for handing down this unique linguistic device that enables the language to be spoken more easily and sound more smoothly.
For without this helpful word ng, Tagalog language would indeed be difficult to speak and would sound terribly wrong making the speaker appear as though he was stuttering. For example instead of saying isang tao (one person) we would utter isa na tao or instead of saying dalawang bagay (two things) we would say dalawa na bagay. Aside from being grammatically incorrect, these mistakes sound too painful to the ears as George Bernard Shaw would have it in the play My Fair Lady.
Look at the number of words being saved when the word ng is used to relate a modifier like an adjective to the noun that it refers to. The phrase taong bundok (person of the mountains) would instead be spoken as tao na nakatira sa bundok. See how awkward sounding a phrase would be if the word ng is not in existence. The title of the Philippine national anthem would be Lupa na Hinirang (the Chosen Land) instead of Lupang Hinirang. A place in Metro Manila called Pulang Lupa (Red Earth) would be called Pula na Lupa.
The word ng is used to relate a modifier to the word that it modifies when the first word ends in a vowel or the n sound. For example say pusang itim (black cat) not pusa na itim but itim na pusa is acceptable. Say maling sagot (wrong answer) instead of mali na sagot. However, sagot na mali is grammatically correct and acceptable. Say balong malalim (deep well) instead of balon na malalim. But malalim na balon would be okay. Say tabing dagat if you want to mean seashore and tabi ng dagat if you want to mean beside the sea.
Say biglang bigla (suddenly) not bigla na bigla or bigla-bigla. Say magandang bulaklak (beautiful flower) instead of maganda na bulaklak. Use the phrase kotseng asul (blue car) not kotse na asul. Use the term kesong puti (white cheese) not keso na puti. Choose to say malayong lugar (far place) rather than malayo na lugar. Say aking damit (my clothes) not akin na damit. But damit ko which means the same thing is perfectly alright. Use the phrase basang basahan (wet rag) not basa na basahan.
Of course there are exceptions to this rule and these are when ng is used to mean the English word of. Even if the word that precedes ng ends in a vowel or the n sound, ng is not connected to the preceding word when it is used in a normal way as a preposition that means of in English. Examples of this include tulo ng tubig (droplets of water), paa ng kabayo (horse's foot), lasa ng pagkain (taste of food), dahon ng halaman (leaf of the plant), huni ng ibon (chirping of the birds), haba ng tulay (length of the bridge), bale ng manggagawa (worker's advanced pay), tae ng aso (the dog's poo), and alon ng dagat (waves of the sea).