Entering an ongoing conversation

Is this blog function the way to get into an ongoing conversation or is that considered a rude interruption?  While I was playing an online game, a conversation was running on the bottom of the screen that I tried to add my two cents to, but even though I was able to compose a comment in a textbox (below the conversation textbox), there was no way that I could find to post the comment.  Help with this would be appreciated!