what's the difference between face to face and face-to-face, and when to use them?

Is this sentence correct:
Last week's lecture was nothing like today's talking face to face/face-to-face.
Last week's lecture was nothing like today's face-to-face/face to face speaking.
You meet face to face, but you have a face-to-face meeting. Use the hyphens when the entire phrase modifies a noun.

“Face to face” is one of those phrases that sometimes confuse people because of it’s “made up” nature, like “one on one”.

I may not be completely correct about the hyphens but this is what I understand.

When the phrase is used as adjective, hyphen is supposed to be used.

When it’s used as adverbial phrase, hyphen is not needed. Other experts may correct me if this understanding is wrong.

Paul and Mary had a face-to-face discussion. (Used as adjective)

Paul and Mary had long discussion face to face (used as adverb)
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so, in the examples I gave earlier, is it face to face with or without hyphens?
so in the example I gave earlier, is it with or without hyphens?
Just like I said in my first post: In the first one, talking face to face.

The second one - face-to-face because it modifies a noun. But your noun choice isn't natural. Try face-to-face meeting or face-to-face discussion.
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Merriam Webster says to hyphenate adverb and adj; AP says to only hyphenate adjective before a noun. Sorry -- pick a style and go with it.
Should be "as I said" not "like I said."