like we play on gambling site and want to withdraw our crypto then we just need to type the amount we need to withdraw and click on "withdraw" button. then our withdrawal request get approved in a second, and goes directly to the blockchain.
my question is what is the process of withdrawal on most of the sites, which is so fast and without any double spending or issue like that?
In simple terms you can create a code in mostly any programming language, all you need is a "node" to compile and broadcast the transaction for the miners to mine and verify the block your transaction is broadcasted in, this process takes a few seconds.