Gosh, where shall we start!
First, any Linux version is free open source, not just Ubuntu. Mainly that's because of how the licence works. A very few companies have attempted to build non-free desktops on top of Linux, but I believe all have failed or been very unpopular.
Ubuntu Linux, which is built on top of Debian Linux, has been hugely successful because of several aspects. They've put a lot of attention into making it easy to use, they've also created very friendly support forums. Neither of those are true for all Linux versions, some are very much for experienced users, or for servers, or embedded devices, or mainframes, and some support forums can be hard for a beginner to get help -- ask a question in a naive fashion and get mocked. Sad, though as Linux gains popularity and years ago became non just for geeks, that kind of treatment has been more rare. In Ubuntu's forums there is a code of conduct, so if anyone is stupid enough to be unfriendly to a beginner, they will be the one pilloried, not the beginner.
Ubuntu has a predictable release schedule (unlike some versions of Linux, which say "it's ready when it's ready!"). Every 2 years there's a 'long term support' (LTS) release, which is supported with security fixes etc for 5 years (the most recent is version 16.04, released in April 2016). There's also more bleeding edge releases every 6 months, but I'd advise you to steer clear until you're more experienced.
Cheaver mentions Linux Mint, that's another good one for beginners, an offshoot of Ubuntu, and with the same friendly values. I like Mint a lot.
However, the
best version for you is the one that some friend or acquaintance is familiar with. You can learn entirely on your own, and with the help of forums and the wealth of material on the web, but it's good to have personal help on hand. Check
www.lug.org.uk to find a Linux user group near you. Oh! I've just realised you're not in the UK, ok, then scratch that idea, but I'm sure there are user groups all over the world.
You ask about applications, but that depends on your interests and needs.
And there's no need to make a jump to Linux straight away. Prepare for it. Use open source programs on Windows (or Mac) that are also available on Linux. That way, when you do jump, the transition will seem much easier. After all, few of us are interested in an operating system for its own sake. 99% of the time that we're using the computer, we're using applications, such as web browsers, mail clients, photo organisers...
If you use Windows, stop using IE or Edge, start using Firefox (I prefer it as a web browser and it's one of the first things I install on a Windows PC). I'd recommend Firefox even if you have no intention whatsoever of moving away from Windows.
Use Thunderbird as a mail client, or if you use web mail of course that's equally available to you on any platform.
Try out LibreOffice, it reads and writes MS docs.
If you're a heavyweight Photoshop user, try Gimp (though there are also less advanced image editors).
And so on. There are plenty of sites that recommend alternatives, e.g.
www.alternative.to.