Suppose I have a transaction hash and it belongs to some transaction which was done on a smart contract. From the hash, how do I determine what was the contract method which was called and with what parameters?
One easy way is to use an explorer. For example see this and click on "Invocation data" and you see that function "breakCookie" was called with the name "Roman". This requires that the author of the contract uploaded their source code, so that names can be determined from the compiled bytecode.