In my Chinese class notes these two sentences appear:
我是南非人 and 我在看节目
Why does the one use 我是 and the other 我在? Is there a rule/guidelines to help me decide which one to use?
Thanks, Jaco
Yes.
是 (verb) means "is, am, are, to be, yes" while 在 (verb) means "at, to be in, to exist", or is a short form of 正在 (adverb,) which is used to indicate an action in progress. 是 is the confirmation of a state of being, whereas 在 is a confirmation of a location, or indicates that you are in the middle of/in the process of doing something.
是 (verb) + noun
So when you want to use "I am [x]" where [x] could be a student/a teacher/an old man/a young girl/a lawyer, that's when you use 是. What comes after it is a noun.
e.g. 我是留学生。你是哪国人?她是我女朋友。
在 (verb) + place name
Where you want to use "I am at [x]" where [x] is a place like Beijing/America/etc., that's when you use 在. What comes after it is a place name.
e.g. 我在北京学习汉语。你在哪儿?他在美国旅行。
正在/正/在 (adverb) + verb
When you want to indicate a continuing action "I am currently [x]" where [x] is a verb like reading a book/watching TV/cooking dinner, you use 正在/正/在. What comes after it is a verb.
e.g. 我正在看电视。你在想什么?她正做饭。
我是 means 'I am something', while 我在 in your sentence is the abbreviation of 我正在, which means 'I am doing something'
English 'be' is a mixture of at least 3 old verbs. That is why it is so irregular.
In Spanish we have the same situation as Chinese: 'ser' = be, am = 是 and 'estar' = be in a place or situation = 在。
English, sadly, formally lost this distinction, but in reality, it is still there.