LIBRE account names are like Twitter account names: short human readable names such as "cryptoguy" or "billsmith" that can be used to create "pseudonymous" identities on chain. They can be anywhere from 1 to 12 characters and can contain the letters a thru z and numbers 1,2,3,4,5. The numbers 0,6,7,8, and 9 are not permitted for technical reasons.
There is no requirement that your LIBRE account name be in any way associated with your real name. You can be "Frank White" and have the account name "bcbny5amqcnt" or "guitarguy". You can easily have multiple accounts. Note that all activity is recorded on the public blockchain, and, just like you wouldn't want your tax information shared with the world, privacy of transactions is generally a good idea.
The Bitcoin Libre wallet has an "i'm feeling lucky" button that will generate an automatic name.