Every single transaction on the blockchain is assigned a unique transaction ID, also known as a transaction hash. Often, the terms can be found with the abbreviations tx or txn substituted for transaction.
Explaining the cryptography behind this number in full would require a few more articles. However, for our purposes, it will do to simply understand this hash number as a condensed form of the transaction's data -- in other words, details such as the addresses involved, the timestamp, and the quantity of tokens exchanged.
Locating the transaction ID is straightforward, and varies depending on the platform you're using to access GPEX Wallet:
As soon as you submit a transaction to the network, it will appear in the Activity tab of your account, detailing whether you were sending or receiving.
Simply click on the transaction in question:
This should display the interface below, at which point you will notice the convenient Copy Transaction ID option. This will copy the ID to your clipboard, ready for however it's needed.
Alternatively, and if you want to see more detail, you could also select View on block explorer, which will take you to the appropriate block explorer page for the network you're using. Here, the transaction ID is referred to as the transaction hash.