Yeats is a name of Celtic origin, which means that the "ea" dipthong should be pronounced to rhyme with rates and weights. In names with an Anglo-Saxon origin, like, for example, Keats, the "ea" dipthong is pronounced to rhyme with words like eats and seats.
"The Lake Isle of Innisfree" is one of Yeats's earlier poems and was first published in 1890, when Yeats was only 25 years old. You can hear Yeats himself reading this poem at the youtube link provided below. The eponymous "Innisfree" is a small island situated mostly in County Sligo, in Ireland, where Yeats spent much of his childhood.
The speaker of the poem wishes to escape from the "roadway(s)" and "pavements grey" of the city, and build himself a "small cabin" on the island of Innisfree. The poem, although wishful, has a rather melancholy tone, which you can hear for yourself if you listen to the aforementioned reading. The speaker dreams of "water lapping with low sounds by the shore," and longs for his cabin in his "deep heart's core"; but, for whatever reason, he seems unable to leave the city. The cabin seems like only a dream and nothing more.