In the first stanza of "April Inventory," it says "In one whole year I haven't learned/ a blessed thing they pay you for." What does this mean?
I believe that at this point the narrator is a baby (maybe 1 year old?), because it takes us through a cycle of life, but I don't understand who "you" is (line 2) and I think that may be the source of my confusion.
I do not believe that you are right about the speaker being a baby at this point in the poem. Instead, he is already a grown man who is a teacher. He will remain this throughout the poem. I would argue that the poem does not take place over time. Instead, I think it is his "inventory" of himself at one point in his life.
What he is saying in the first stanza is that he is getting older (will soon have no hair) and yet has not gotten ahead in life in any tangible way. He is expressing some amount of unhappiness because he has not learned anything that has economic value.
The line you cite is about that idea. It is about the idea (that will be fully fleshed out as the poem goes along) that the speaker has not had material success in the world. He has not learned things that "you" (meaning people in general) get paid for. Instead, he has learned and taught things that make him a better person. He has taught someone how to love and has figured out how to know himself (to "name my name").
So when the speaker says he hasn't learned anything "they pay you for" he is talking about his inability to get ahead in a career.