Q: what's mean? modifiers of noun とはどういう意味ですか?
A: The modifier of a noun is gives information about a noun. A noun is a person, place, or thing. A modifier of a noun can be an adjective— (blue, pretty, happy, friendly, sharp,) or it can be a phrase. It gives information about a noun.

The ANGRY fish swam in circles
The dog THAT STOLE MY SANDWICH is over there
Laura is the LOVELY woman DANCING WITH FRED.


Q: Sometimes the modifier may be placed after the noun if the verb or context permits it. A modifier placed after the noun describes the resulting state of the action expressed by the verb or by the context.

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Q: "Speak softly love ",is "softly" the modifier of "love" in grammar,why and why not?
A: I don't think "softly" modifies "love" here ("to love softly" doesn't really make any sense, and if those two words WERE a pair, then having "speak" in front would not make sense). It's more likely that the sentence should look like this: "Speak softly, love." In this case, "softly" modifies "speak", and the person talking is calling somebody else "love" as a pet name and telling them to "speak softly"