The main sentence is, I`ll tell you. When am I going to tell you? When I see you. Thus, “I`ll tell you” is incomplete without confrontation “when I see you.” The main sentence, as I said, is the main sentence. What did I say? That I`m busy. “I`m busy” is incomplete, without “I said.” I may not be busy, but I said it was me. Note that many of these conjunctions must be followed by the subjunctive. The main clause is that I can`t leave. Why can`t I go? Because I have no money. The idea here is not that I don`t want to leave, but the fact that I can`t leave because I don`t have any money. Como no tengo dinero, no puedo ir. – Since I don`t have any money, I can`t leave. Te lo diré cuando nos veamos.
-I`ll tell you when I see you. The subjunction of conjunctions follows dependent (subordinated) clauses with main clauses. You can see a dependent clause because it cannot be left alone — its meaning is incomplete without the main clause.