Siri is Apple's voice-controlled personal assistant and she, or he, has been around for a few years now. The assistant first appeared on the iPhone 4S and it was described by Apple as the best thing on the iPhone during the launch presentation. Twice.

It's fair to say she, yes we are going with she in this feature, has probably now lost that claim as the iPhone now does a lot more than it did back then, but Siri has developed with age. Her intelligence has grown and her abilities have expanded. She has also had to keep up with or fight off Microsoft's Cortana and Google Now.

So what is special about Siri? What is she able to do, how does she do it and what can she help you with if you are an Apple user? Well, we are going to tell you. Here is everything there is to know about Siri. The whole shebang.

As we mentioned, Siri is a built-in, voice-controlled personal assistant available for Apple users. The idea is that you talk to her as you would a friend and she aims to help you get things done, whether that be making a dinner reservation or sending a message.

Siri is designed to offer you a seamless way of interacting with your iPhone iPad or iPod Touch by you speaking to her and her speaking back to you to find or do what you need. You can ask her questions, tell her to show you something or issue her with commands for her to execute on your behalf, hands-free.

Siri has access to every other built-in application on your iPhone - Mail, Contacts, Messages, Maps, Safari, etc - and will call upon those apps to present data or search through their databases whenever she needs to. Ultimately, Siri does all the leg work for you. It means you can carry out a single task by just saying "Hey Siri" or double tapping the Home button, rather than open multiple apps or spend time writing messages or finding contacts.

Siri can do a lot. She's pretty damn clever and sometimes she is quite funny too. If you want to get a giggle out of Siri rather than ask her to do something serious, then have a read of our separate feature that you can find here

Otherwise, Siri can help you when you're out and about, with sports and entertainment information, phone calls and messages, getting organised, tips and tricks and of course getting you answers.

At a glance, she will read your last email, text your friend to tell them you're running late, shuffle your road trip playlist on iTunes, let you know what films are playing today, find a table for three in London, call your dad at work. She can also tell you where a good indian is nearby, flip a coin, find books by a specific author, set an alarm, give you directions and even set a reminder that can activate only when it recognises that you're in or have left a certain location ("Pick up dry cleaning", when you leave work, for example).

That's not all though, in fact, it probably isn't even half. She'll tell you what the weather is like tomorrow, move meetings, tell you when the next game is for your team and you can even get her to roll a die, along with a series of other things such as teach her how to pronounce your name or tell her which of your contacts are family members. We told you she was pretty smart, and that's without any of the new functions that have been introduced with iOS 9.

Siri got even smarter with iOS 9. As well as everything we mentioned above, you'll be able to ask Siri to get an app from the App Store, show you your selfies from New Year's Eve, find pictures from your trip to New York or get public transit directions to the Guggenheim Museum.

The other big new addition is HomeKit. You'll be able to create scenes with HomeKit and ask Siri to set them for you. For example, you could dim the living room lights and turn on the TV with one voice command.

Siri is based on the based on the fields of Artificial Intelligence and Natural Language Processing, and it is comprised of three components - a conversational interface, personal context awareness and service delegation.

The conversational interface is about how Siri understands you in the first place. The general workings of the straight word-for-word voice recognition have to be good in order to hear what you're saying but deciphering the meaning is all down to statistics and machine learning, which is where the personal context awareness system comes in.

There's a huge amount of work in Siri that can predict what you're getting at based on key words that you use, as well as your general habits and language choice. She is designed to adapt to your individual preferences over time and personalise results.

The service delegation system is the unbridled access to all of the iPhones built-in apps and their inner workings. This access is how Siri does what she does. Without the access, Siri would be a pretty rubbish assistant.

When Siri first launched, she only recognised and spoke French, German, US English, Australian English and real proper English English. God save the queen style. This is no longer the case. Siri has been travelling and she is now fluent in lots of languages.

She can speak and understand English (Australia, Canada, India, New Zealand, Singapore, UK, US), Spanish, French, German, Italian, Japanese, Korean, Mandarin, Norwegian, Cantonese, Swedish, Danish, Dutch, Russian, Turkish, Thai and Portuguese.

Siri is available for iPhone 4s or later, iPad with Retina display, iPad mini and iPod touch (5th generation or later). If you don't have one of these devices, or you are on Android or Windows Phone, then Siri won't be your friend.