GP didn't use the word conspiring, I did. But to answer your question, conspiracy is an expression of intent. It can be merely speech but usually involves some action to back up the speech. Because, again, conspiracy is a question of establishing intent.

For example, three people discussing plans for a bank robbery are conspiring. Likewise, the same three people sharing only a knowing glance before splitting up and regrouping with masks, guns, a car and a map with the local bank circled have also conspired to rob a bank. One group only spoke and the other didn't speak, yet both conspired.