Right off the bat, the poem's speaker tells his beloved that he's a poor guy. He doesn't have anything to give her… except his poetry. Doesn't sound like much, does it? Well, that's why the speaker spends the rest of the poem explaining to his beloved just how valuable his poem is.
A poem may be just a bunch of pretty words, but it can do a lot, according to this speaker. He compares his poem to a coat, or a pair of socks that can keep his beloved warm in winter. He compares his poem to food. He compares his poem to a scarf. He says his poem is like a guide that can help the beloved find her way when she's lost. And, in the final stanza, he makes a pretty bold claim: his poem is the only thing that his beloved needs to live. And all of this is punctuated by the speaker telling his beloved that he loves her. All together now: aww.