When Mac developer Casady & Greene sold its audio player, SoundJam MP, to Apple at the turn of the century, it couldn't possibly have imagined what would become of its poster child. Within a year it had been transformed into iTunes 1.0, then used as a launch pad for the very first iPod, and history was made.

Today, iTunes is a true giant among Apple applications - a massive, multi-platform colossus that bestrides millions of Macs, PCs, iPhones, iPods and iPads. It has helped turn Apple into one of the world's largest entertainment retailers.

And very soon it'll become an internet phenomenon too, thanks to the launch of iCloud and iTunes Connect - two new services due later this year and next, which will give you easy access to all the content you own, wherever you may be.

Of course, iTunes has only been able to become ubiquitous because of what it can do. You can use it to buy, rent or download music, movies and TV shows; listen to podcasts or thousands of internet radio stations; buy books; subscribe to magazines; and keep your iOS device loaded up with tons of clever, innovative and exciting apps that will keep you entertained at home and away. And, of course, it's free.

Indeed there's so much to iTunes that it can be tricky to know where to start, whether you are a new or experienced user. So we've put together this essential guide to help you get the best from iTunes, from the very basics to advanced tips and tricks, with particular emphasis on the key features of iTunes 10 and synchronising your stuff using an iPad, iPod or iPhone. Ready? Let's dive right in…

What iTunes is, what it does and how it can benefit you…

Because iTunes can do so much, it can seem daunting to use at first - there are so many options, tabs, sidebars and buttons to choose from. But when you break it down, it really is quite simple to get to grips with and you'll soon find yourself adding and enjoying content without a second thought.

One of the best ways to figure out what's going on is to look at the Source sidebar on the left of the iTunes window. Here your iTunes library is divided into different sub-sections - Music, Films, TV Programmes, Podcasts, iTunes U, Apps, Ringtones and Radio - and it's where all your media content is organised.

Below that is the Store section, which enables you to go shopping for new music, movies, and so on, using the iTunes Store, and to engage in some music-oriented social networking with Ping.

And you'll also find Genius, which helps you discover old favourites and new media. And, finally there are Playlists, which gives you different ways to enjoy your stuff by slicing it up into manageable, customisable chunks.

At the Source

You can listen to or watch anything that's in your library using the Source sidebar. Selecting any one of the options reveals relevant content in the middle window (the browser). This is where you can see, explore and play all the stuff in your library.

But what do you do if you can't find anything under Music or Films? You next step is to import or 'rip' content from media you own already, such as music CDs. The other option is to use your new iTunes account to do a little shopping at the iTunes Store.

Importing a music CD couldn't be easier - it will automatically appear in iTunes when you insert one into your Mac's optical drive and iTunes will scurry off to the internet to fetch details about it from the Gracenote online music database.

You can edit any details (these are known as ID tags or metatags) it finds by selecting a track or multiple tracks and selecting Command+I. You can also add in your own cover artwork either by scanning it in manually, doing a Google search or using the power of the iTunes Store.

iTunes imports songs using the same audio codec as the iTunes Store - 256kbps AAC - although you can easily change this by selecting Preferences > Import Settings from the iTunes main menu. Here you'll find a wide range of audio codecs to choose from - including MP3, WAV and Apple Lossless, although iTunes doesn't support more exotic codecs like Ogg Vorbis or FLAC.

To all but the most sensitive of ears, 256kbps AAC is virtually indistinguishable from CD quality and offers the best compromise between sound quality and storage space. Your mileage may vary.

Album artwork

To get album artwork from the iTunes Store you'll need to use either an existing Apple ID or an iTunes account (the two are usually interlinked); failing that, you'll have to create a new one.

Do this by selecting Store > Create Account from the iTunes main menu. Once you've done that you can import album artwork by going to the main menu again and selecting Advanced > Get Album Artwork.

Signing up for an iTunes Store account has several other benefits, of course: you can use it to buy and download a huge range of current and back-catalogue albums, music videos, books, movies and TV shows. You can also use your iTunes Store account to get a whole bunch of free stuff, from promotional singles and movie trailers to hundreds and hundreds of podcasts. You can even listen and watch study materials, courtesy of some of the world's leading universities, via iTunes U.

Moving pictures

Movie and TV content on iTunes is often available in both standard definition (640x480 resolution) and high definition (1280x720p) versions, with 1080p content rumoured to be available later this year. Watching HD content on the small screens of the iPhone or 11-inch MacBook Air may not be all that beneficial, but you can easily hook them up to an external monitor or a TV to make the most of the picture quality.

Neither do you have to buy movies outright - the iTunes Store also gives you the option to rent a whole range of films. You can store a rented movie on your Mac for up to 30 days without watching it, but once you do, you only have 48 hours to watch the remainder otherwise it will magically disappear.

Talking of the iPhone, we can't mention the features of iTunes without also including one of the main reasons why it exists at all: its close integration with iOS devices such as the iPhone, iPod and iPad. Setting up, managing and filling any of these devices with content is almost always done via iTunes, although that looks likely to change later this year with the introduction of iCloud.