The poem is framed as an "Epitaph on a Tyrant": a summary of the personality and legacy of an unnamed dictator. The dictator is most likely dead, but there are other possibilities, too. For example, he might be deposed, and this might be an "Epitaph" on his political career.
The speaker and dictator are unidentified, and the setting is unnamed. As a result, the poem makes a political statement that transcends any particular place or time. It was written during the rise of fascism in 1930s Europe, but it could apply to any of countless dictators throughout history: it's a comment on the nature of tyrants and tyranny in general.
The speaker first says that the tyrant's goal was "Perfection, of a kind." This is a dryly ironic statement, and the caesuras after "Perfection" and "kind" add to its carefully hedged tone. The tyrant's goal was "Perfection" as he defined it, but his definition wasn't one most people would associate with the word. It's implied that "what he was after" was an ideal society: his ideal society, not anyone else's. He wanted total control over his country, the way perfectionist artists want total control over their work. He worked to shape his whole culture around his own power and ego—and get rid of anything that hindered that fantasy.
In service of his dark goal, he "invented" a kind of "poetry" that "was easy to understand." The word "poetry" here might be partly literal, but it's mostly figurative. It seems to be a metaphor (or synecdoche) for all the propagandistic art and literature with which the tyrant flooded his country. Dictatorial regimes typically use very simplistic ("easy to understand") anthems, logos, chants, works of art, etc. to push the leader's narrative, flatter the leader's vanity, and secure the leader's power. Together, these efforts amount to a kind of popular art or "poetry," lacking in the complexity, nuance, and humanity of real poetry. Its popularity may be organic, enforced, or both: in any case, it's "easy to understand" both for those who support the regime and those who oppose it. Its message is blunt: obey and glorify the leader.
Again, the poem imagines the tyrant as a kind of evil version of an artist or writer: one who bullies and manipulates all of society into following his narcissistic vision. (Some dictators have even started out as literal artists or writers; for example, Hitler was a painter as a young man, Stalin a poet.)