These phrases mean two different things , right ?

Yes. I'm glad this has been brought up.

Being a nice person is very different to being a nice guy.

There is a mentality in the community that you need to be a bad boy, or someone who doesn't give a shit about the girls he interacts with and treats them like dogs. You go to RSD Julien's youtube page and see him saying things like you should call girls dogs and then you go out and it doesn't work. Why? Because being a bad boy is not what gets the girl.

Now a bad boy may be the polar opposite of a nice guy, but both extremes are bad. One is too positive, the other is too negative. Where can you find the balance? In the middle obviously. But what does that mean?

Being a nice person is being kind to girls, being genuinely kind and honest. At the same time you are playful in a nice way, with a smile on your face. When you tease she knows you don't mean it. You are kind yet firm. That is a much nicer way to see the game. Be a nice person who is firm with the girl. Who doesn't take her shit, who doesn't suck up to her. Someone who appreciates her fully but won't give in to her demands. If she continues to demand things you just walk away. That's why the best punishment you can give a girl is to walk away, or to pull your attention away from her. Being offensive when she is mean can work in a frame battle, however if she persists with being rude you just walk away. Beat hatred with love. That should be a common mantra in the community but unfortunately it isn't.

Be firm in your kindness, be firm in you desire to her, be firm in your appreciation towards her. That's what being a nice person is.

Be a decent person, not a "nice" person. Decent is a lot more grounded and full of integrity.

"nice guy" - placating behavior/always puts others' needs above his own, has a weak attachment w himself (undifferentiated) looking to find security in the next available woman he has even a slight interest in, engages in a lot of social references tactics to 'check-in' that what he does was 'good' (always seeking external validation).

Confident guy (much better descriptor than "nice person") - does things for others for giving's sake and nothing more (without expectation of anything in return), has a lightness about him because he doesn't need anyone else to validate WHO he is based on WHAT he does, is in touch with his needs and knows how to have them met or at least asks for it in a confident manner how others can help meet those needs, is more responsive than reaction because he doesn't adjust like a chameleon to whatever the other person's perceived reaction may be from moment to moment.

being a photographer and taking photos is the same thing right?

nice person, nice guy, it sounds the same to me. except in one case it could be a woman too, and nice guy is only concerning men. or what?

They are the same thing.

Big/large, small/tiny, nice person/nice guy...

Why do you care? This just seems like a pointless discussion.

nice person - is when you are really nice not just actions but in personality and if you mean to say this,and that you really meant it (definitely in a good way).
while in nice guy, you are just like looking good to the community. like going out with better guys but not good guys. (like your cool or something)

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Honestly, I forget all about the "nice guy" and "Nice person" crap. Why bother caring which category you fall into? Just don't bend over arseways to make her or anyone else happy. If you respect yourself and can be a decent or "nice guy" to a woman she's only going to admire you all the more. Also, don't alter your behaviour around her: You're who you are, not what you think women want you to be.