Usually the first word in a sentence is a verb and aloha means love as either a noun or a verb. The next word is the subject of the sentence, and it may be spelled either au or wau, meaning the first person singular pronoun in the subjective case, I. In general au is more common, but both are considered acceptable. In some expressions wau seems to flow better, at least for some people, and this is one of the expressions where wauis not as uncommon as for general expressions.
The last word ʻoe is the second person singular pronoun, you—by itself the subjective case. The preceding iā makes the pronoun to be in the objective case (direct object, or adding the sense of to or toward). Sometimes you will see the two words combined into one as iāʻoe. It should be apparent at this point the expression means I love you.