Good morning!

I was studying the use of articles and I have some questions.
1. I saw that when I have uncountable nouns I can use some, but it's not necessary. Example: "May I drink water" or "May I drink some water". Am I right?
2. And when I have countable nouns I always need to use a/an/the/my..., but I have a question. When I don't know if it is Countable or Uncountable is there any way of using another structure. For example, the dictionary says that "salad"is Countable or Uncountable, so if I say: "Last night I ate salad", "I ate a salad". Which is right? Why?
3. Do English people really follow all this structure? It's really confusing.
Thanks.