user70780: I know is related to these:
What is the rationale behind Bitcoin mining?
Why do we need Proof of Work in bitcoin?
But I don't fully understand those answers, and I think usually is much easier to understand the concept if we know the problem it solves.
So, what will happen without mining and proof of work on Bitcoins? in a step by step example.   
From what I understand mining is put a time and node limit to the block creation. Because if every node on the chain is allowed to create a new block at any time then we will have a lot of conflicts.
Is that the reason for mining? to limit the block creation?   
And why some people say it avoids double spend?
EDIT: when I say mining I actually mean the proof of work, and all the rules (like block interval) about mining, I know mining is for validating blocks, but why we need the proof of work and made in that way (solving a difficult hash) and why we are limiting the blocks to 10min. What will happen if we allow blocks to be added every second with much easier hashes to solve for example? what will be the problem with this?

user85: Suppose Alice has one bitcoin. She can form a transaction to send that bitcoin to Bob. And she can also form a transaction to send that bitcoin to Charlie. Somehow, we all have to eventually agree that one of those transactions is valid and the other is not. Why?
Suppose Alice can't possibly convince Bob that she paid him that bitcoin because Bob always worries that the transaction sending the bitcoin to Charlie will be considered valid. That would make bitcoin entirely useless as nobody could ever act on a payment. For example, suppose Alice is paying for a book. When would Bob send her the book?
Suppose Alice can possibly convince Bob that she paid him that bitcoin. But what would stop her from also convincing Charlie? The situation is symmetric. So what if she buys a book from Bob for one bitcoin but also a book from Charlie for one bitcoin but pays with the very same bitcoin? Are there now two bitcoins where there was one before? Do some people think Bob has the bitcoin and some think Charlie does? How would that work?
We need some way to know with a high degree of confidence that every honest actor will eventually agree that one of those transactions is valid and one of them is not. Once that happens, the person who received the transaction we all agree on can send Alice the book and we will all know that they now have the bitcoin. This ensures payment finality at some point and continued agreement of coin ownership.
Mining is how bitcoin does this.

user133697: Because you need to timestamp every block and this action can not be free of charge. Otherwise every node would create a block and try to cheat with wrong timestamp.
From the Bitcoin white paper:

To implement a distributed timestamp server on a peer-to-peer basis,
we will need to use a proof- of-work system similar to Adam Back's
Hashcash [6], rather than newspaper or Usenet posts.


70780: <p>I know is related to these:<br>
<a href="https://bitcoin.stackexchange.com/questions/3174/what-is-the-rationale-behind-bitcoin-mining">What is the rationale behind Bitcoin mining?</a><br>
<a href="https://bitcoin.stackexchange.com/questions/51286/why-do-we-need-proof-of-work-in-bitcoin">Why do we need Proof of Work in bitcoin?</a><br>
But I don't fully understand those answers, and I think usually is much easier to understand the concept if we know the problem it solves.<br>
So, what will happen without mining and proof of work on Bitcoins? in a step by step example.   </p>

<p>From what I understand mining is put a time and node limit to the block creation. Because if every node on the chain is allowed to create a new block at any time then we will have a lot of conflicts.<br>
Is that the reason for mining? to limit the block creation?   </p>

<p>And why some people say it avoids double spend?</p>

<p><strong>EDIT:</strong> when I say mining I actually mean the proof of work, and all the rules (like block interval) about mining, I know mining is for validating blocks, but <em>why</em> we need the proof of work and made in that way (solving a difficult hash) and why we are limiting the blocks to 10min. What will happen if we allow blocks to be added every second with much easier hashes to solve for example? what will be the problem with this?</p>
 85: <p>Suppose Alice has one bitcoin. She can form a transaction to send that bitcoin to Bob. And she can also form a transaction to send that bitcoin to Charlie. Somehow, we all have to eventually agree that one of those transactions is valid and the other is not. Why?</p>

<p>Suppose Alice can't possibly convince Bob that she paid him that bitcoin because Bob always worries that the transaction sending the bitcoin to Charlie will be considered valid. That would make bitcoin entirely useless as nobody could ever act on a payment. For example, suppose Alice is paying for a book. When would Bob send her the book?</p>

<p>Suppose Alice can possibly convince Bob that she paid him that bitcoin. But what would stop her from also convincing Charlie? The situation is symmetric. So what if she buys a book from Bob for one bitcoin but also a book from Charlie for one bitcoin but pays with the very same bitcoin? Are there now two bitcoins where there was one before? Do some people think Bob has the bitcoin and some think Charlie does? How would that work?</p>

<p>We need some way to know with a high degree of confidence that every honest actor will eventually agree that one of those transactions is valid and one of them is not. Once that happens, the person who received the transaction we all agree on can send Alice the book and we will all know that they now have the bitcoin. This ensures payment finality at some point and continued agreement of coin ownership.</p>

<p>Mining is how bitcoin does this.</p>
 133697: <p>Because you need to timestamp every block and this action can not be free of charge. Otherwise every node would create a block and try to cheat with wrong timestamp.</p>
<p>From the Bitcoin white paper:</p>
<blockquote>
<p>To implement a distributed timestamp server on a peer-to-peer basis,
we will need to use a proof- of-work system similar to Adam Back's
Hashcash [6], rather than newspaper or Usenet posts.</p>
</blockquote>
