Is the UTXO associated with output and Tx id?
Yes, you're exactly right, each UTXO is basically just a tuple (txid, output_index). Then when that output is going to be spent, you refer to it by listing the tuple as an input.
Essentially, that's why they're called "Unspent Transaction Outputs" (UTXOs), not "Unspent Transactions".
For example, look at this random transaction output I pulled of of the block chain:
(Note that 1 is the index, meaning it's actually the second output)
Then when the transaction is spent, the input references this previously unspent transaction output.
ID of spending TX: 57149f629790e61a5fbab9e27041858ada6348aa17323c15b9da9659b90717bb
"txid" : "564bb87efc20751dde182b678e848ceaa75ac54fd2eab33808842f40e953f7e6",
"vout" : 1,