Dropbox is a cloud storage service. In cloud storage, you files or data is stored on their cloud servers and can be accessed from anywhere, all you need is an internet connection. Dropbox is one of the simplest cloud storage solutions available.
Just download the application on your computer and store your documents or anything in the dropbox folder, wait for it to sync to the cloud. Now you can access your from anywhere on any device. Just install the application or app on another computer or mobile device, login with the same credentials and your files will be synced to that computer. No need of any configurations. You can also share files and folders with your friends. You can collaborate your works friends, which is very nice.