Node.js asynchronous function, process.nextTick()

I'm writing a node backend and I'm a little confused how should I deal with async functions. I've read about process.nextTick(), but how often should I use. Most of my code is based on callbacks, like database calls, which are asynchronous by themselves. But I also have a few functions of my own, that should be async.

So which one is a good example of async function?

function validateUser1(user, callback) {

  process.nextTick(function() {    

     //validate user, some regex and stuff

     callback(err, user);

  });

}

function validateUser2(user, callback) {

  //validate user, some regex and stuff

  process.nextTick(callback, err, user);

}

function validateUser3(user, callback) {

  process.nextTick(function() {    

    //validate user, some regex and stuff

    process.nextTick(callback, err, user);

  });

}

I don't know whether I should wrap everything in process.nextTick , or wrap just the callback? or both?

And overall, the idea with node.js is to write lots of small functions rather than bigger ones, and call them asynchronously to not block other events, right?

via Maciej Krawczyk