You don't need much to start using a Web OS right now. Once you've chosen a service, just visit its site from any Internet-connected desktop or laptop computer and sign up for a free account. After a quick registration, you'll be staring at your new virtual desktop for the first time.
While the interfaces for different Web OS services vary slightly, they tend to follow the basic layout that Windows popularized. In G.ho.st, the taskbar runs across the bottom of the screen just as it does in Windows, and a Go button is located where the Start button would be. You'll also find a Quick Launch bar just to the right of the Go button, and a system tray to the far right of the taskbar.
The G.ho.st desktop gives you rapid access to a few of the most important features of your virtual machine, including a link to all of your programs, the control panel, mail, and an instant messenger application that supports AIM, Google Talk, ICQ, MSN Messenger, and Yahoo Messenger. Want to get started with a text document or spreadsheet right away? Launch Zoho Writer or Zoho Sheets directly from the desktop and start typing. You might also try the 'Take the Tour' link on the desktop, which will get you oriented quickly.
Assuming that you don't plan on using your Web OS as your primary PC all the time, you'll want to start managing your files intelligently from the moment you log on. While you certainly can just upload files from your desktop to the Web OS one by one, or even in batches, the better approach is to use the built-in syncing features to manage files on all your machines automatically.
In G.ho.st, you'll find the appropriately named Sync utility, available in both Windows and Mac versions from the Ghost Services menu. Select the version for the computer you happen to be using, and download and run the installer. Afterward, enter your log-in info and set the options as you see fit. The best choice is to sync in both directions and set conflict resolution to keep the newest version of each file. You can also choose to simply append "~deleted" to the file names of old versions, which can prevent you from losing important data if something goes wrong.