hash – What is TXID? Is it used to calculate Merkroot?

I downloaded a block template containing ‘data’, ‘txid’, and ‘hash’ for each transaction. I read some articles that Merkelroot is calculated using ‘txid’. Is it true? Why does txid not hash, and what is the difference between the two? Before today, I always used a hash to calculate the merkleroot, which gave me a “bad-txnmerkleroot” error message. If I need to use the txid, how do I find the txid of the Coinbase I built on?