The poem reads like a set of commands, as if the speaker is giving orders to someone, or perhaps to themselves. The language comes from housework: flatten, straighten, iron. But the thing being pressed is a mind. The speaker wants the "surface of your understanding" smoothed out and the "dreadful drunkenness" ironed away, which suggests some kind of muddled, careless way of thinking that needs fixing.
The twist comes in the last line. After all that flattening, the goal is to learn "how round the world can be." It's a neat contradiction: you flatten things in order to discover roundness. One way to read it is that clearing away confusion and narrow assumptions lets you see the world as fuller and more complete than you thought.
The tone is stern, almost bossy, yet there's a dry humor in the ironing image. The mood is brisk and a little playful, with a quiet hope underneath that clearer thinking will widen the view.