Wa Particle and 'am'.

My friend and I are having a debate over the particle 'wa' or は. I told him that this particle in average usage has no real definition and acts as nothing more than an emphasizer that the word it comes after is the subject. For instance, ねこは 'neko ha' translates literally to 'cat'. The 'wa' doesn't get translated, because it doesn't have a definition. It just emphasizes that in an anticipated sentence, 'neko' would be the subject of the sentence. I use the following sentence for example: これわわたしのねこです・ (kore wa watashi no neko desu?) that should literally translate to 'this my cat.'

My friend says that 'wa' doesn't have a definition by itself. However, he says that when it comes after a pronoun, that it means the conjugated form of the verb 'to be'. For example, he thinks that あなたは translates to 'You are' when, I believe, realistically, that just translate to 'you' with 'wa' indicating that 'anata' is the subject of the sentence. I tried to explain that if he wished to say 'I am' or 'you are' then he would have to include the indicative 'equal' particle 'desu' or です at the end.

Does わたしは by itself mean 'I am' or does it mean simply 'I'. I tried to explain that わたし (watashi) and あなた (anata) are merely 'building block words', as I explained, they take on their 'pronoun' forms only when you add the particles at the end, like so:

watashi wa = I, subject
watashi o = me, direct object
watashi ni = me, indirect object
watashi no = my, posessive

Is this correct or am I mistaken? I'd like to know. I don't want to learn Japanese incorrectly.

You are right, your friend is wrong. Saying that wa=am is saying that wa equals the verb "to be", which for anybody that knows anything about Japanese knows that the verb comes last in a sentence and that verb is "だ、です、である、でございます" etc. not は. Your friend is simply thinking about Japanese in English, I remember thinking the same thing when I first started learning but soon realized i was wrong.
は is generally a topic marker or used for emphasis in a sentence.