About a year ago, we switched from DropBox to Microsoft's OneDrive (formerly SkyDrive) primarily because OneDrive had evolved to pretty well match all of the core functions of DropBox but offered substantially higher levels of storage on all tiers, free and paid. As of this writing, OneDrive provides you with 15 GB of free storage while DropBox provides only 2 GB (you can increase both limits in 0.5 GB increments with referrals to other people you know). Additionally, if you install OneDrive on your smartphone and turn on the "Camera Roll" function (more on that below), you'll get an additional 3 GB of storage space. Need more space? OneDrive gives you 100 GB for $1.99 per month, 200 GB for $3.99 per month, and a whopping 1 TB for $6.99 per month (this is actually part of the Office 365 Personal subscription service). By contrast, DropBox's only other individual price tier provides 1 TB of storage for $9.99 per month (and this obviously doesn't include any of the goodies from an Office 365 subscription).
Now presumably, you already have a whole pile of files and folders on your computer hard drive. Unless you're backing them up periodically, they are at risk of digital death should something bad happen to your hard drive (e.g., fatal crash and, yes, we speak from experience) or your computer (e.g., you shouldn't share that glass of wine with your computer). This is where the OneDrive downloadable application comes in. After you have your OneDrive account set up, go to the OneDrive download page (https://onedrive.live.com/about/en-us/download/) and download and install the OneDrive application on your computer. This will add a OneDrive folder to your computer's hard drive. Anything placed into that folder will be automatically synchronized to OneDrive. You can grab the entire collection of your hard drive based folders and files and drop them into the OneDrive folder and the synchronization of those folders and files with OneDrive will begin (if you have a lot of stuff, you might want to go out and get a bite to eat because the initial synchronization of all of it may take a while). After that, any update you make to a file or folder contained anywhere within the OneDrive folder will be automatically synchronized to your OneDrive.
But OneDrive is more than simply a file backup tool. If you install the OneDrive application on another device (another computer or a tablet or a smartphone), you'll be able to access your files on that device too (note that you'll have limited editing capability for documents on mobile devices that don't have Office or an Office type set of apps installed). If, for example, you have a computer at home and one at work both with the OneDrive application installed and accessing your OneDrive account, you can update a document on your work computer, come home, open the same document on your home computer and it too will be updated (yep, welcome to the wonderful world of synchronization). So, no more emailing documents to yourself. Your OneDrive cloud drive contains the one true version of each of your documents. You can share individual files and folders with anyone you wish and can specify their level of access (read only, read-write) and even whether they need to have a Microsoft account or not in order to have access. You can also access your OneDrive from any other computer through a browser (just go to http://onedrive.com and sign in).
If you use a Windows PC and are using one of Microsoft's email clients (the Windows 8 Mail client, Microsoft Outlook, Windows Live Mail) and want to email a collection of photos, you can choose to temporarily use a portion of your OneDrive space to store those images in the cloud. So, instead of emailing your images as file attachments (which can make your email very bulky), you'll be sending out a link from which your email recipients will be able to view (and download if they wish) the photo set during that temporary period (90 days). Recipients can even kick off a full-screen slideshow from that OneDrive photo bucket. This is a very slick and well thought out feature.
While we're generally not the biggest fans of Microsoft, we have to admit that OneDrive is a giant pile of awesome and you'll have a very difficult time finding anything substantively better. If you are not currently taking any steps to nominally backup your files, you should install OneDrive for at least that function. But OneDrive is much more than a file backup tool and it is very highly recommended for both ease of use and immense functionality.