Basically, a cloud storage is a virtual space you can access via an internet connection and where you can upload your data. You can upload your music and video files, photos, word docs or any other valuable documents you want to keep safe. Depending on the cloud storage you can either upload only music and video files, other documents or all together. MP3tunes for example, offers a space where you can only store music and videos, while on Dropbox you can upload any type of digital document. It depends on what you are looking for.
For my music collection, for example, I am using the MP3tunes cloud. I can store both audio and video files in the MP3tunes Locker. You can also try it out if you're interested in securing your music collection, I know that the 1st 2GB of storage space are offered free of charge.
I prefer using the MP3tunes cloud together with Audials. It's a soft that enables you to record streaming music and videos, convert files, rip DVDs etc. and besides that, it has an export feature which lets you connect to your cloud account and manage your files without opening your browser. For me, it makes things a lot simpler, I can just download or record some music and videos with Audials and then directly upload it on my cloud storage.
And you can take a look at this tutorial on how to manage your MP3tunes music collection using Audials, if you are interested:
Anyway, enough with the chitchat, I hope my answer was helpful!