Nostr usernames can indeed be a bit different from what you might be used to on other platforms. Here's a breakdown of how they work:

1. **Public Keys (Hexadecimal Strings):**
   - Every user on Nostr has a unique public key, which is a long string of characters (typically in hexadecimal format). This key is used to identify users on the network.

2. **NIP-05 Identifiers:**
   - Nostr Improvement Proposal 05 (NIP-05) introduces a way to map these public keys to more human-readable identifiers, similar to email addresses. These identifiers look like `user@domain.com`.
   - The domain part of the identifier is a domain name that hosts a file mapping the human-readable identifier to the public key.

3. **Username@Domain:**
   - Some users choose to use NIP-05 identifiers, which look like `username@domain.com`. This is more user-friendly and easier to remember than a long hexadecimal string.
   - To get one of these, you need to have access to a domain where you can host the necessary mapping file. There are services that can help set this up for you, or you can do it yourself if you have a domain.

4. **Username Only:**
   - Some users might appear with just a username, which could be a display name or alias they've set up in their client. This is not a unique identifier and can be shared by multiple users.

### How to Get a NIP-05 Identifier

1. **Own a Domain:**
   - You need to own a domain or have access to one where you can host a file.

2. **Create a Mapping File:**
   - Create a JSON file that maps your NIP-05 identifier to your public key. The file should be hosted at `https://yourdomain.com/.well-known/nostr.json`.

3. **Example JSON File:**
   ```json
   {
     "names": {
       "yourusername": "yourpublickey"
     }
   }
   ```

4. **Configure Your Client:**
   - In your Nostr client, you can configure it to use your NIP-05 identifier. The client will then use this identifier to link to your public key.

By following these steps, you can set up a more user-friendly identifier on Nostr. If you need more detailed instructions or run into any issues, feel free to ask!