@AbhasKumarSinha Again,
read the tag description. The
set-theory tag description says "This tag is for set theory topics typically studied at the advanced undergraduate or graduate level. These include cofinality, axioms of ZFC, axiom of choice, forcing, set-theoretic independence, large cardinals, models of set theory, ultrafilters, ultrapowers, constructible universe, inner model ... " Is there a single topic in that list that you understand?