Dropbox, SkyDrive, Google Drive, the list of online sync and storage services is growing, but not all of them are compatible with Linux. This may one reason why Ubuntu has its own online storage and sync service along the lines of those mentioned above. Ubuntu One is free to join and you get 5Gb of online storage, synced with one or more folders on the local disk drive. What's more, you can access it from your Windows PC too.
The first step is to sign up with the service and you need to go to the Ubuntu One website using a web browser. An easy way to do this in Ubuntu is to click the Ubuntu One icon in the Launcher and click Learn More in the window that is displayed. At the website, click the sign up link and then New Account button. You only need an email address and password.
When you have an account at Ubuntu One, you can install Ubuntu One in Linux and Windows. In Ubuntu click the Ubuntu One icon in the Launcher and click Install. Everything that is required is already present. After installation, click the button to sign in.
Ubuntu One creates a folder in your home folder called, naturally enough, Ubuntu One. The contents of this folder are kept in sync with the contents of your online storage space and any other computer with Ubuntu One on, including Windows PCs. Other folders can be included in the sync and there's an option to add them at the end of the installation. Don't try and sync everything though. In fact, you may not want to add any extra folders and just have the Ubuntu One folder synced.
As with other folder sync services, you can access your files from any computer with a web browser and an internet connection. Just log in at the website. However, installing the Windows software from the Downloads page of the Ubuntu One website is the best way. The Windows software is the same as Ubuntu and offers the same options on installation - sync the Ubuntu One folder and any any others that you want to sync, like Documents, Pictures, Music, Videos and so on. The Ubuntu One folder is in your own folder - C:\Users\YourName. It's an identical copy of the one on your Linux PC.
Ubuntu One has more features in Ubuntu than in Windows. For example, you can right click a file, select Ubuntu One, Publish, which makes it publicly accessible to anyone on the internet. Right click it again and you can copy the web link to the clipboard so you can paste it into emails or elsewhere. You can also right click a folder and select Ubuntu One, Share. You are prompted to enter another Ubuntu One user and then they will be allowed to access the contents of the folder. There's a tick box to determine whether they have write access in addition to read access.