Now to a very simple decision. Do you want your story to take place in the past, the present or the future? Let's deal with the last option immediately, since it really won't take long. Let me tell you the answer: probably not, if you want to be published as commercial fiction. There's always someone out there who'll disprove the obvious one day. But books are rarely set in the future. As a narrative tense it's too odd and too constricting. For a short story that screams 'disconnect' from the outset... possibly. A full-length novel? Best avoided.
Which leaves us with two basic choices...
Few books use the present tense throughout. It's not as odd as the future tense for a narrative, but it's not far off. It can also become distinctly wearisome after a while. Narrative tends to run to a rhythm, much like a piece of music. It will have fast and slow passages, loud and quiet ones. At times characters will be ruminating on the past or the future and giving the reader a chance to do the same in the context of the story so far. At other points the book will be making the story happen, moving more quickly, furiously even. It's very hard to achieve that sense of a changing tone if all you have to work with is the present tense. It's much like the first-person point of view in that respect, which is one reason why first-person passages often work best when set in the present tense.
There's a clue to one of the most useful functions for the present. Imagine your novel is principally written in the past tense. From time to time your protagonist has dreams or flashbacks which start to illuminate the mystery as it's revealed. The sudden jolt of the present can make these interludes more gripping.
It's way past midnight and I'm walking down the alley to the pier. Butcher's Lane, they call it. Sally's round here somewhere I think. Lost and frightened. Maybe. Or something else. Something I don't want to think about. ...
Most novels are written in what grammarians call 'the simple past tense'. Don't you love that word? Simple. Books are meant to look that way to the reader. Authors are there to deal with the complexity, then hide it underneath the carpet.
Grammarians also call it the 'preterite', which doesn't sound simple at all though it's exactly the same thing - the tense used by most authors most of the time. Stories recount things as they happen. The reader's perspective is that of a remote viewer witnessing a series of events.
Charlie went to the pier.
Sally ran away.
Later the two of them met by the railway station.
Simple past. Readers who don't even know what tense is, and probably think a preterite is something that falls from the sky, understand instinctively what's going on when you write like this. ...
You will use other variations of the past in your book. There's the past continuous:
Charlie was swimming towards the pier when the wave hit him.
And the past perfect:
Sally had thought for a while that it was time to go back to the water. Then Charlie called and finally she knew.
The past simple is the predominant voice of fiction, one you've been listening to all your life if you're an avid reader. My advice to the first-time writer is: don't buck the trend. Assume your book will be written in the lingua franca. Play with the present from time to time if you feel like it. Drop into other forms of the past tense when the demands of good plain English demand.