That mean if I am a miner can I add my transaction to candidate block?
Yes. If you are a miner, you can preferentially choose your own transactions to be added to your candidate block.
What is the main use if Candidate block?
Every miner will produce their own candidate block, and then attempt to mine it by calculating the block hash. The miner who is successful first will broadcast their candidate block to the blockchain.
This next block to be added called Candidate Block?
Once a candidate block has been verified and added to the blockchain, it is just known as a block. All other candidate blocks will then be invalid, and the process will start again with miners generating new candidate blocks and attempting to find a valid hash.
Is there any article where I can read more about this?
Try here:
https://www.binance.vision/glossary/candidate-block