Either use the browser or a chat client.
Explaining the browser is easier:
1. click on the irc link at the menubar on top of the page
2. a new window opens where you give a Nickname
3. click Connect
4. when it connects you type the stuff into the input area at the bottom of the page.
Additional information:
- if you close the page, all the convos will be lost, it has no "memory" so to speak
- you can write private messages to users just like with every chat client, like discord (these will be lost too when page closes)
- if the thing lose connection there might be issues with reconnecting with the same name (the server will think for a couple of minutes the same username is still connected)
- stuff
Ask your answers.