It's a way of reporting what someone said about something that someone else said.
Here's a breakdown:
* Como: "as" or "how"
* dice: "says" or "tells"
* que: "that"
* dijo: "said"
Example:
* "Mi amigo dijo que la película fue aburrida, como dice que dijo su novia."
* Translation: "My friend said the movie was boring, as he says that his girlfriend said."
In essence, it's a way of indicating that someone is relaying information they heard from another person. It can also be used to highlight the indirect nature of the information, suggesting that it might not be entirely accurate or reliable.