This is an extremely heavy philosophical text which is not for beginners or those unfamiliar with continental philosophy.
The basic thesis Agamben advances is that sovereignty (hence state power) is constructed through the exclusion (which is simultaneously an inclusion-as-exception) of "bare life", which is to say, the body and relations of force. This exclusion returns in the figure of sovereign power (as law-making and thus as excess over law) and its construction of homo sacer, a type of subject who can be "killed but not sacrificed" (and who is thus outside both profane and sacred law). Homo sacer reaches his apogee in the camp, such as Nazi concentration camps. The camp is the "paradigm" of the modern state, and homo sacer and the "state of exception" in which the state suspends basic rights is becoming the normal condition of politics.
There are several problems here. The first is that Agamben is prone to argue by assertion and exegesis. The result is that his claims are largely unsupported and "take it or leave it" - either you're convinced by his account or you aren't. The second is that he doesn't draw political conclusions from what is obviously a political subject. If the state of exception and homo sacer are inherent to state sovereignty as such, Agamben's thesis would seem to be a powerful case for anarchism, yet he never draws any such implication, nor addresses the corresponding question of how else bodies can be "politicised". Thirdly, the thesis isn't really as original as Agamben seems to think - it's a repetition of themes arising in the work of A. Hirschman, John Zerzan, ecofeminists such as Robyn Eckersley, the Frankfurt School (e.g. Adorno and Horkheimer's "Dialectic of Enlightenment"), and a host of other authors dealing with the exclusion of the "natural", the emotional and the embodied from masculine, industrial, or public institutions. An engagement with such prior literature would have strengthened Agamben's case, not least in allowing him to show how his thesis differs from theirs, and what precisely is added by ideas such as homo sacer and bare life.