As a non-native English speaker, one of my greatest trouble is using proper English tenses. Since there is no verb tense in my native Chinese, I am a little bit like a color blind person trying to convey something I do not deferentiate well. In school we were taught a bunch of grammar rules. And in practice I also go with gut feeling. A lot of times I cannot explain what my gut feeling says by the grammar rules I have learned.
The grammar rules are like this. To say things happen at present, use present tense. To say things that happened in the past, use past tense. Simple, huh?
Well, actualy nothing in human language is simple. It turns out it is also correct to say things happened in present tense. The are choices of narrative tense and the concept of implicatures to consider. So you can use present tense to describe things happened in the past. And it conveys some subtle difference in meaning.
Confusing? Very. I guess the game is to keep training my gut feeling until it works.