How extensible is the tonal quality rule? I'm starting a Chinese languange course now, I've just seen that ma can have four meanings, it depends only on their tonal qualities.

I wonder: How extensible is this tonal quality rule in forming new meanings? Is there a rule where only a few syllables can have different meanings?
Like others have told you, you might be confused a little bit. First of all, while languages have words made of syllables, Chinese has characters where each character is a syllable. These syllables can be written using the Latin alphabet with some systems, Pinyin being the most common one. Syllables can have 5 different tones: high, rising, fall-rising, falling and neutral.

According to the syllable and the tone attached to it, you can have a different meaning (excluding the fact that many characters cannot stand alone).

If you write "mā", it doesn't necessarily mean "mother", since that Pinyin transcription can refer to different characters. For example, the characters below are all read as mā:



The one on the left-center is the Traditional form for 妈, which means "ma, mamma". 

Not only that, the same character can have different readings, which means different meanings. But also in the same reading, we have different meanings! See the character 着 for example:



As you see, 着 has 5 different readings, but much more meanings, even for one single reading. I know this might scare you from learning Chinese, but once you start, you'll get used to it.