Just about every major web application and/or service now offers cloud storage (Google, Microsoft, Adobe, Linux, etc). Cloud storage is simply a place where you can upload your data to a remote server, giving you access to your data from anywhere on any device.
Microsoft OneDrive is part of the Microsoft Office Suite, it is their version of cloud storage. It's legit but if you don't need it, don't bother with it.
I use Google Drive myself, I received 125GB of free storage with a mobile device upgrade.