There's lots of detail in wikipedia pages: Pink Floyd, Dark Side of the Moon and Down & Out, but here's my interpretation: Pink Floyd's music contained many concepts, relevant here are the ones "Exploitaion and Oppression" and "Alienation, War and Insanity". Roger Water's father had died in action in the 1939-1945 war and the lyrics refer to the cost of that war, and wars in general. The expression 'us and them' refers to the sociology concept of Ingroups and Outgroups. Here there are two examples: the front line soldier who is sacrificed while the officer class (the General) sits back and looks at maps. Then there is the old soldier (assumed) begging for a cup of tea and bread from the passing busy commuter. (Inequality of sciety). He dies of neglect and starvation. 'Us and Them' is also often used in discussions of class. Us being the working class/proletariat (ordinary men) and them being the ruling class. This is another concept common in Pink Floyd's music. Round and round and .... may refer to shots from a gun, insanity, or a round in music (ok it's all three). I could carry on line by line, but you don't want it totally dissected, do you?