I was reading "Song of the Open Road" by Walt Whitman and I completely did not understand the poem. Can someone explain it to me with lots of details?

Much of understanding this poem is understanding to things: 1) The title and 2) Walt Whitman.

Lets talk Walt Whitman first.  He was a true Romantic in the sense that as a writer he championed all the ideals of the Romantic era of writing.  He glorified nature and the human spirit.  He championed democracy and "seeking" soul.  He believed in the beauty and the power of the human spirit.

Now look at the title.  "Song of the Open Road" is a poem that glorifies the idea of going out on the open road in search of those things that I mentioned in the previous paragraph.  Whitman suggests that we are all:

He asks his readers to come along:

Allons! whoever you are, come travel with me!

 /

Traveling with me, you find what never tires.

On traveling the open road, Whitman says that there is much beauty, peace, and wisdom to be found.  He does not suggest that it is an easy road - indeed he calls it a "struggle" - but he does say that it is a "sufficient" for all humans need.

Going by sections, Whitman uses Section 1 to announce his purpose to travel with no burdens upon him.  In Section 2, he invites his reader along by telling us that no one in judged on the open road.  It is open to anyone.  In Section 3, Whitmas suggests how the open road is a great equalizer.  Not only is everyone welcome, but everyone is treated equally by all things - the light, the pavements, the town.  It is "all evident and amicable with me."

In Section 4, he professes his love for the open road, and says that by being so welcoming to him, the road helps him to welcome others.  For Section 5, he announces the freedom he gets from the road.  In Section 6, he tells us that wisdom is to be found in that open freedom, more than in classrooms.  In Section 7, he makes that wisdom less intellectual and more spiritual, suggesting that he can find the answers to the larger questions of life, and the connection between all human souls.

In Section 8, Whitman makes all this talk of freedom and wisdom and soul-searching more personal by saying that it will all bring happiness - therefore, the open road brings happiness.  In Section 9, "he says the earth never tires", suggesting that there is no limit to this happiness, and no time too late to start on the path.  Section 10 raises the stakes by making th ejourney more adventurous, more urgent.  He does this by reminding readers that the earth never ends, but humans are mortal.

Section 11 reminds us that it is soul richness, not material wealth, that will be gained.  Section 12 employs the "bandwagon" technique by saying that great ones of the past have travelled the road before.  Section 13 continues it by suggesting that many current souls are out there, too.  Section 14 makes the road travel a metaphor for soul travelling.  Sections 15, 16, and 17 then build to the urgent rhetorical questions, convincing the reader to answer yes:

Will you give me yourself? will you come travel with me?
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Shall we stick by each other as long as we live?