English Grammar has a lot of rules about when we don't use articles. Here are four of them:
We don't use an article:
1. to talk about plural and uncountable nouns or when talking about things in general:
I'm terrified of heights
2. before countries, towns, streets, languages and single mountains:
I'm from China.
3. Before some places and with some forms of transport:
4. In exclamations with what + uncountable noun:
What beautiful weather!