user97892: I have read that a block contains several transactions. 
An attacker can forge fake a block.
The blockchain is safe because the system will choose and keep the longest chain.
So the fake block will be lost.
This is great but what happens if my transaction was included in the fake block?
Let's suppose I am buying a car. Should I wait for 6 confirmations to be sure? That would mean that I have to wait one hour!

user13866: 
what happens if my transaction is in the fake block?

It is also in the memory pool (mempool) of pending transactions at other nodes run by more honest people and will be included in a new and valid block in the normal way.

Let’s suppose I am buying a Tesla car. Should I wait 6 blocks to be generated to be sure? But I have to wait 1 hour!

Yes.
There are faster payment methods for Bitcoin - e.g. Lightning Network (LN) and arguably perhaps escrow services. But they have their own trust model and characteristics you need to understand when using them.

user5406: 
An attacker can forge fake block.

Yes, but an invalid block would be rejected by all other participants that see it, and not relayed. Thus, such a block has little to no impact.

This is great but what happens if my transaction is in the fake block? Let’s suppose i am buying a car. Should i wait 6 blocks to be generated to be sure? But I have to wait one hour!

A transaction is a signed payment order to the Bitcoin network.
As long as it remains a valid instruction set to the network, it will be tracked and distributed by network participants to include in a block. From the perspective of nodes following the best chain, being included in a block that is not part of the best chain is equivalent to not being included in any block at all. Thus, an invalid block including a transaction has no impact on any nodes that recognize the block as invalid–they still consider the transaction unconfirmed and they will continue to consider it for inclusion in another block.

97892: <p>I have read that a block contains several transactions. </p>

<p>An attacker can forge fake a block.</p>

<p>The blockchain is safe because the system will choose and keep the longest chain.</p>

<p>So the fake block will be lost.</p>

<p>This is great but what happens if my transaction was included in the fake block?
Let's suppose I am buying a car. Should I wait for 6 confirmations to be sure? That would mean that I have to wait one hour!</p>
 13866: <blockquote>
  <p><strong>what happens if my transaction is in the fake block?</strong></p>
</blockquote>

<p>It is also in the memory pool (mempool) of pending transactions at other nodes run by more honest people and will be included in a new and valid block in the normal way.</p>

<blockquote>
  <p><strong>Let’s suppose I am buying a Tesla car. Should I wait 6 blocks to be generated to be sure? But I have to wait 1 hour!</strong></p>
</blockquote>

<p>Yes.</p>

<p>There are faster payment methods for Bitcoin - e.g. Lightning Network (LN) and arguably perhaps escrow services. But they have their own trust model and characteristics you need to understand when using them.</p>
 5406: <blockquote>
  <p>An attacker can forge fake block.</p>
</blockquote>

<p>Yes, but an invalid block would be rejected by all other participants that see it, and not relayed. Thus, such a block has little to no impact.</p>

<blockquote>
  <p>This is great but what happens if my transaction is in the fake block? Let’s suppose i am buying a car. Should i wait 6 blocks to be generated to be sure? But I have to wait one hour!</p>
</blockquote>

<p>A transaction is a signed payment order to the Bitcoin network.
As long as it remains a valid instruction set to the network, it will be tracked and distributed by network participants to include in a block. From the perspective of nodes following the best chain, being included in a block that is not part of the best chain is equivalent to not being included in any block at all. Thus, an invalid block including a transaction has no impact on any nodes that recognize the block as invalid–they still consider the transaction unconfirmed and they will continue to consider it for inclusion in another block.</p>
