I can't figure out how to be able to talk to each other using cloud variables, could someone explain it to me?

Sorry, what do you mean? Are you making a chatroom or are you trying to link to projects together?

Are you talking about a chat?

This is very difficult. You could search for a tutorial on Youtube.

If you want to know how you can put strings into cloud variables:
https://scratch.mit.edu/projects/11210130/

I mean I want to know how to put a chat box in a game

You need to use a white list of acceptable words or phrases. If you use a list to store these you can potentially just store a string of digits to a cloud variable - eg 005234078 represents list items 5, 234 and 78 (it's much easier if you make them all 3 digits assuming you don't need more than 999 possible words/phrases).

However you also need to understand how multiplayer works so you can control which player is managing which cloud variable (see my project for an outline of one way of doing this https://scratch.mit.edu/projects/89449465/ ) and if you want to store usernames you also need to understand how to encode and decode those - http://wiki.scratch.mit.edu/wiki/Global_High_Scores shows how to do this.

working on it