It may daunt someone, but it is only going through by exhausting range of study enables one to comprehend crux of IR theories and underlying concept in international interactions (political, economic, social, cultural, and, above all, strategic), books by Baylis, Kegly, and Goldstein are conducive in this regard.

we may discuss in detail these theories (if someone interested), but now I just inform you the essence of these theories.
constructivism: constructivist employ social science to demonstrate how norms, practices, ideas, and identities play a crucial role in IR which is neglected by mainstream theories (realism and liberalism).
post-modernism: highlights the hegemony of western ideas in IR , it is fundamentally a rejection of existing theories with the argument that truth is not universal it is socially constructed.
for instance, it challenges the very idea of the realist that power is the military strength instead they argue ideas, norms and words may more crucial form of power.