Her main message, or meaning in the poem is just simply one of longing. She expresses a romatic desire to be with someone, free to love and be loved, and do what they want. She feels that her heart is in port, just sitting there, waiting, useless. She longs to set sail, to be "Rowing in Eden" on "the sea!" with the object of her desire. It is a romantic longing that she expresses, and longs for the "luxury" of "wild nights" moored with her love.
As for figurative techniques, she employs a metaphor (comparing two things that have similar qualities). She compares her rather boring, stagnant life to "a heart in port" and she expands that metaphor when she says a heart in port doesn't need a compass or chart because it isn't going anywhere. This helps to emphasize her frustration with her situation; she feels stuck, powerless, and useless. Another technique that she uses is allusion (referring to other sources); she refers to Eden, which is from the Bible. This symbolizes what she feels being out, free, and with her love would be like, which is ultimate paradise.
As always, Emily Dickinson is short, but sweet, and uses her style and concise figurative techniques to relay the message and mood of her poems.
Some people actually say that "Wild Nights" is very erotic and about sexual passion and rapture. Here, the poem is about desire, as the speaker longs for a companion or lover. The speaker is believed to be male ("moor in thee").
Here is what a source says about the poem:
Dickinson is undoubtedly using "luxury" in a meaning she found in her 1844 dictionary, one which is no longer used: lust, voluptuousness in the gratification of appetite. The "heart in port" is the lover's embrace. Yielding themselves to sexual passion, they have no need for compass or chart, which are used to get to a specific destination and are instruments of control and reason. The sea is a common image for passion; think of the romantic movies you've seen with the waves crashing or the famous scene with the lovers in the waves in From Here to Eternity. "Rowing" and "moor in thee" are, in this reading, sexual intercourse.
This poem can also be about a religious enlightenment with the lover as God.
Christian mystics (people who communicate directly with God) often describe the joy they feel while communicating with God in language which modern psychoanalysts see as sexual; for example, mystics speak of rapture and ecstasy during their union with God, and they cry out to God, "stab me" or "pierce my soul, oh Lord." On the other hand, the number of feelings human beings can experience and the vocabulary with which they can express their experiences is limited; using the same language to describe a spiritual experience and a sexual experience does not necessarily mean that both experiences are sexual.