This questions is a bit ambiguous, so I'm going to assume you're asking about the kinds of themes, ideas, and so forth that are present throughout Milosz's works.
Milosz's background is important in understanding the themes present in his work. Milosz is Polish, and he grew up among the political upheaval of World War I and II. He spent a lot of his childhood in Russia under the Czarist government. As an adult, Milosz worked in the underground resistance movement in Warsaw. He eventually left Poland to escape the oppressive Communist government that took power after World War II.
The fact that Milosz was surrounded by political upheaval, warfare, and corrupt government regimes heavily influenced his work. In his essay The Witness of Poetry, he writes, "My corner of Europe, owing to the extraordinary and lethal events that have been occurring there, comparable only to violent earthquakes, affords a peculiar perspective. As a result, all of us who come from those parts appraise poetry slightly differently than do the majority of my audience, for we tend to view it as a witness and participant in one of mankind’s major transformations.”
Milosz's poems are often written in a tragic and cynical style. His first book, Poem of the Frozen Time, deals with the violence leading up to World War II. Important themes in his poetry include death, loss, suffering, the cyclical nature of violence, and the value of human life in the face of this violence.
Milosz also moved around quite a bit in his life, most often because of political upheaval. In the 1970s, he moved to California and became a US citizen. As a result, other themes in his work include flight, migration, belonging or not belonging, and new beginnings.