This is a sentence from Death Note. The assassin has just said "I am victorious!" thinking his plan to kill everyone was successful. But being alive and still, the detective says:

あなたはさっき、自分の勝ちを宣言しましたが、確かに 本来 あなたは勝っていた。私は負けていました。

I clearly, by context, understood that the last part of the sentence is a Third Conditional. What would have happened if...

But I don't actually know how to produce this grammar. Or even recognize it without the help of context. Since all I see is the use of past continuous tense.

If I want to make my own sentences, let's say: If I had studied more, I would have passed my university entrance exams... What kind of grammar would I have to use?

Please, teach me, folks!