How Do Attackers Forge Bitcoin Blocks And How Do You Identify Forge Bitcoin Blocks? I have read that a block contains several bitcoin transactions and an attacker can forge fake blocks.

Does these forged fake bitcoin blocks cost the attackers money for mining or was it just generated for free from the attacker node?

The blockchain is safe from attacks because the blockchain was programmed by Satoshi to validate and keep the longest chain. 

So the forge block will disappear from the blockchain network. This is wonderful but what happens if an attacker forge bitcoin blocks?  

I even read that some of these forge blocks can have 2 to 3 confirmations. Is this true?

So how do you identify these forge bitcoin blocks immediately?
I assume that when you say an attacker can forge blocks, you mean that a dishonest miner can create invalid blocks.

The answer is no for a very simple reason. When a miner's bitcoin node (the computer which runs the bitcoin software) creates a block, it must follow all of the consensus rules. Let's say, for example, he tries to create a coinbase transaction with 13 bitcoin, plus fees. Note that, at the time of writing this, the block reward is 12.5 bitcoin.

Then it finds Proof of Work and sends the block to the rest of the network. Every node that receives this block will first check if it follows the rules. Since it doesn't, the node will reject that block. Therefore, it will not get included in the blockchain and the miner just lost the reward.

So, every node validates everything on its own. No node trusts information it recieves from other nodes.