If you receive any amount of on-chain bitcoin in a single tx - that is one UTXO.

If you received two separate txs, you now have two UTXOs.

A UTXO can be any amount.

Let's say you received two tx in your wallet, each worth 100,000 sats.

Your wallet shows a single balance of 200,000 sats. In reality, you have two UTXOs worth 100,000 sats each.

Let's say you want to spend 150,000 sats from this wallet. The wallet will take both UTXOs, spend them, and return 50,000 sats to you, which is a new UTXO that you now own. (Note that I haven't included the tx fees in this example for demonstration purposes.)

There are wallets that allow you to choose which UTXOs you spend and even label them. This is important when you start using coinjoins. If you mess up by sending certain UTXOs together, the common ownership will be revealed and this could destroy your privacy.