1- is the blocks can only contains one transaction or more ?
Blocks can contain as many transactions as the 1MB block size allows. Usually Miners will add transactions to the proposed block until the 1MB size is filled, in order to collect the maximum transaction fees possible.
2- we know that the miners doing calculation through POW ? is it the same calculation of the hash tx ?
No, it is not the same. What miners do within the POW is following:
- They hash all the transactions they have added to the proposed block obtaining a No.
- Then they generate a random no also called a nonce. This nonce is then hashed together with the above obtained hash. They repeat step 2 until the obtained hash is smaller or equal to the network difficulty target. As the hasing process is non deterministic they literally try as many combinations as they can. (brute force). That’s why the miners computing power is measured as Hashes/second. (actually TH/s - terahash per second).
The network aims at an average block generation time of 10min. So it will adjust the difficulty target , up (means easier to guess) or down (harder to guess) depending on how the miners perform
3- is the block that is created by a miner doesn’t valide untill it is validated by all the miners in the network ? is that correct ? and how it is considered as a valide block ?
Once a new valid block has been created by a miner it is distributed in the network by the nodes. As the network is a world wide network and it takes some time for all nodes to be in sync it can happen that more miners manage to propose valid blocks and there are several proposed blockchain ledgers passed around. In this case there is a “temporary network split”. As more blocks are being produced on version of the blockchain ledger will be mined faster and therefore will be longer than the others. The network takes this into consideration and will always accept the longest chain and discard all the others. Usually it is considered that a transaction is valid (permanent) when it is hashed in to a block that has other 3-4 blocks already stacked upon it and the risk of this chain being discard in favor of a longer one is considered to be minimal.
4- is every miner considered as Node in Bitcoin Network ?
No. Miners and nodes are different. Miners are responsible for block creation, though POW and thus adding the valid transactions to the blockchain ledger making them permanent. Nodes are responsible for maintaining the network. They validate the created blocks, they store the entire ledger and distribute it throughout the network, they acknowledge transactions and create a list of all pending valid transactions for the miners to get.
I hope this helps.