Sending information from the client to the server?

I'm trying to create a Custom chat gui and I have everything finished so far, the only problem is that I need a way to send information from the client to the server. The game is filteringenabled, and the chat gui doesn't rely on the roblox chat gui, thus I disabled it. My question is, is there a way to send the text on a textbox from the clients side to the server and how is it done? In order to make the gui work all I need to do is have the text from the gui that's changed on the client changed to the server, which I'm not sure how to do. I've searched everywhere I could, youtube, here, google, forums, and I still haven't found anything that's worked or helped.