Arabic words ending in tâ' marbûTa (ـة/ة) are usually of feminine gender. It looks like a combination of hâ' (ه) and tâ' (ت). It always comes at the end of the word.
tâ' marbûTa has two ways of being pronounced:
1- When the word is said by itself, it is pronounced as an 'h': zawjah (زَوْجَة).
2- If you add on a grammatical suffix or iDâfa takes place, it is pronounced like tâ': zawjati (زَوْجَتيِ) = my wife; zawjat 'aHmad (زَوْجَة أَحْمَد) = wife of Ahmad
Although it is incorrect, some people while writing informally may write Tied Ta' as Ha'ـه/ه. Also, in Egyptian Arabic and many other dialects of Today's spoken Arabic (I'm not sure but I can say all of the dialects excluding Standard Arabic), it is always pronounced as ha'هـ. (Called heh in Egyptian Arabic. Ta' marbutah is called teh marbutah in Egyptian Arabic.)
1- You can make Tanween to a Tied Taa', but you can't make Tanween to a Haa'. Because of their sense of Arabic, this fact is sometimes used by students (or, at least, taught to them) to help them know whether a word ends in Taa' marbutah or Haa'. When a sentence ends in taa marboota only then,the last letter is silenced for waqf,so it changes into haa.