"I do not forgive him."
Translation:Eu não o desculpo.
I like their method of teaching. They do things which play on our natural tendencies to use them to our advantage. They had the thing with hearts that they phased out (if you've been around a while you'll remember that) probably because people were so emotional when they lost hearts and complained about it. You began a study session with three hearts and if you completed the study session with all your hearts you got a lingot (does anyone care about their lingots anyway). People would miss a question and lose a heart (No lingot for you!) and they'd complain. The folks at DL probably got tired of hearing about it, though it gave added incentive (which increases focus) to complete a study session without error.
What we have now, getting a question wrong with the gameshow buzzer sound and a red x also plays on our emotions. It's a motivator. I think we uptake information better this way rather than being handed a perfect encyclopedic list of all the grammar and lexicon without error and being expected to stay motivated all the way through.
No. From my understanding, "desculpo" always means "I forgive". Perhaps you were thinking about the use of "obrigado" by men and "obrigada" by women? This is a common mistake. "Obrigado" translates literally as "obliged", so describes someone (the person who is obliged, who in this case is the person speaking) and that's why it has a gender. "I oblige" would be "obligo", and wouldn't change for males or females, like in the current example. If you were describing a person you could say "ele está desculpado" (he is forgiven) or "ela está desculpada" (she is forgiven), but that's a different type of sentence. If you were describing yourself, a woman would say "estou desculpada", but again, this means "I am forgiven". I hope that gets to the heart of your question
You must keep in mind who is doing the verb, and conjugate it for them. In this example, who is not forgiving? I am not forgiving. So we conjugate the verb desculpar for eu (Eu não desculpo). Finally, we specify who we aren't forgiving, which is "a" for her and "o" for him as was explained, which results in "Eu não a desculpo." What you wrote is literally "I does not forgive her." Sounds weird, huh? Be careful with your conjugations.
That basically means "I don't forgive himself," which doesn't make sense. We will cover these in a later unit. The gist if it though is when you use reflexive verbs, the subject will perform the verb to itself. The translation almost always includes "-self" (myself/yourself/himself/herself/ourselves/themselves). If someone or something is doing the verb to someone/something else, don't use the reflexive pronouns.
Having read through the discussion I now have a clearer understanding of 'o' or 'a' used in this sentence. (Obrigago! Eu entende!) However, I'm with Pablo in that this concept was not taught very well in the previous lessons. Maybe duolingo should put a few more questions into their previous lessons that cover this topic more thoroughly.