Tell me about a method by which current and voltage can be found out from any circuit, no matter how much complex the circuit is.

there are so many methods, it depend on the circuit.. some methods are Kirchoff current law, Kirchoff voltage law, thevenin therorm, nortan therorm...

dear use Kirchoff's law

Kirchoff law ....usefull

use KCL and KVL it's one of the basic method which is used to solve every complex circuit