Subordinating conjunctions join dependent (subordinate) clauses to
main clauses. You can recognize a dependent clause by the fact that it cannot
stand alone - its meaning is incomplete without the main clause.
1. Dije que estoy ocupado. - I
said that I am busy.
The main clause is I said. What did I say? That I am busy.
"I am busy" is incomplete without "I said." I might not in fact be busy, but I
said that I was.
2.Como no tengo dinero, no puedo ir.
Since I don't have any money, I can't go.
The main clause is I can't go. Why can't I go? Because I
don't have any money. The idea here is not that I don't want to go, but
the fact that I can't go since I don't have
3. Te lo diré cuando nos veamos. - I
will tell you
when I see you.
The main clause is I
will tell you. When will I tell you?
When I see you. So "I will tell you" is incomplete without the
juxtaposition "when I see you."