"I understood what you just said."
Translation:J'ai compris ce que tu viens de dire.
Why do you need 'ce que' and not just que? And why 'de dire', is it because of the viens?
"Ce que" is indefinite. It refers to an unstated or unspecified thing or idea.
- J'ai compris que tu viens de dire quelque chose. = I understood (the fact) that you just said something.
- J'ai compris ce que tu viens de dire. = I understood what you just said.
As for the recent past, (to have just done something), the construction is
- conjugated venir + de + infinitive
Viens does not mean “come” in this case. Viens de + verb means to have just done something. So “tu viens de dire quelque chose” means “you just said something.”