Past, Present, and Future Tense are used to describe three different styles of writing. Past Tense is for anything that has already happened, Present Tense is for what is happening now, and Future Tense is for what is about to happen.
Generally, you will write in Past Tense, with a bit of the other two thrown in. For example, the majority of Cursed Yoshi is written in Past Tense. The exception is that the characters talk in present tense, as to them, things are happening at that time, whereas for us things have already happened.
For example; you might say that 'They walked along the road' rather than 'they are walking along the road' or 'they will walk along the road', assuming it's the narrative. If the characters are talking, they might use one of the other two depending on the situation and whether what they're talking about is happening or will happen.
The only time you'll write narrative in Present Tense will be if you're writing a CYOA Story - Choose Your Own Adventure. One of those stories where after each passage, you choose an option and go to a different page, rather than reading the book as normal. The only conceivable circumstance where you'll use Future Tense would be if you were writing out a prediction by an oracle, for example, but that's not really narrative.
Most words change from tense to tense - 'We did' becomes 'We are doing' which becomes 'We will do'. You need to remember which one to use for each tense.
When you're writing a story, it's a very bad idea to switch tenses partway through the narrative, as it tends to lead to general confusion on the reader's part.