How do I store photos on the net?

When enabled, photos are transferred automatically.

Caveat: if you delete a photo locally (when iCloud Photos is enabled), it will be deleted everywhere.

Some additional, related reading:

Use iCloud with Photos on your Mac - Apple Support

Archive or make copies of the information you store in iCloud - Apple Support

How to back up your Mac - Official Apple Support

I think you have a misconception. iCloud does store date, but it mirrors the data on your device. iCloud is NOT for storage as such. If you use it fo your back up or storage, you will eventually be upset when you loose data. You need to back up your data to an external device or you can pay for on line storage from other vendors.