This is the 7365th most frequent Catalan word.
armar
"Armar" means "to arm" or "to assemble/build" in English.
In this sentence, 'armar' is used to mean 'to stock or equip', specifically referring to equipping the library with books.
Vaig armar la biblioteca amb nous llibres.
I stocked the library with new books.
Here, 'armar' is metaphorically used to mean 'to spark or initiate', indicating inducing or creating an occasion for discussion or debate.
Ell sempre sap com armar un bon debat.
He always knows how to spark a good debate.
In this case, 'armar' implies 'to prepare or assemble', referring to putting together all the requirements or arrangements for the party.