Restore individual apps from a full backup
adb restore always restores the full content of an Android backup file. Therefore if you want to restore apps individually you have to make individual backups so that you get one backup files per app:
adb backup <packagename> -f <packagename>.ab
Alternatively you can use Android Backup Extractor (abe) to convert an Android backup file to an TAR archive, modify that archive (e.g. delete all data and apps you don't want to restore) and then convert the TAR archive back to an Android backup via abe.
Getting the package name of an app without using a Android device
If you want to know what package name has a particular app you can simply use Google Play Store web site. Search for the app you want to know the package name of - for example Twitter.
Check the address bar of your web browser and you will see
The package name comes after the
id= section (it ends at the next
& character or the end of the address). Therefore the package name of twitter is