There are different ways to do this but a very simple and easy way is with Dropbox. Home - Dropbox
This app puts a folder on each mac (or iOS device) you have and syncs the folders with a folder online. When you finish working with a document and save it, it will sync on all your devices.
iCloud will do the same but not with all kinds of documents, only with certain Apple apps.
There are also third party apps that will sync folders over your local network.
I use dropbox.