How to free up storage on iPhone/what is iCloud?

Ok so I have the iPhone 4S. I have over a thousand pictures that takes up almost all my storage. I don't want to delete these pictures or transfer them to a computer. I was wondering if I could like put them all on/in iCloud then delete them off my phone to free usage. I don't have an iCloud and have no idea how it works. If I'm not able to put them in/on iCloud and delete them off my phone, do you have any ideas on how I could deal with my storage issue?

For 1000's of pictures just offload all to your computer