The cloud is just a "hard drive" on the internet. It makes it so that you can access your documents, pictures, and other things on multiple devices.
For instance, say you had some knitting patterns that you wanted to use and found them while on your chrome book. You can then save them to the cloud, ie your "hard drive" on the internet as a document, or series of documents, what have you.
However, for some reason, when you wanted to access the patterns, you didn't have access to said chrome book. You can whip out your handy dandy smart phone and access the place on the internet, known as the "cloud", and thus, have access to those patterns.
The Cloud is also really quite convenient for those of us who have Kindle Fires and have bought a lot of TV shows and movies to watch on it, but don't have enough space on the Kindle Fire's hard drive to store them all. As long as you have access to the web, you can have access to as many movies and TV shows etc, that you can afford space for on the Cloud.
If you aren't techno savvy, or born later than the 80's such concepts would probably not be programmed into your very being, and thus, seem unnatural to use. My mother is often asking me to help her send pictures via text message, or to access some other function (or functions) on her phone for her, as she has noticeable difficulty with learning how to use it. She calls herself "technically challenged". She can't even figure out how to access her Google account to download apps onto her phone via Google Play. I probably should help her with that someday.
I, on the other hand, can maneuver around my smart phone like its second nature, and seeing that it's the same model as hers (with different cases to help distinguish them apart), it helps me to help her when she needs it.