There are multiple ways to perform backups and restores on NetScaler. Usually you perform those backups for disaster recovery if the NetScaler corrupts, or you are performing an upgrade to NetScaler. You can manually backup and restore NetScaler configurations using the GUI, CLI, or you can use Citrix Command Center and NetScaler MAS to perform automatic backups and manual restores.
Backup and restore using GUI and CLI.
Navigate to System -> Backup and Restore -> Backup.
Specify a name for the backup and either Full or Basic backup.
Basic: Backs up configuration files only. These are the files that will change most often so you should consider frequently taking a basic backup of the NetScaler:
Folders and files that are backed up include /nsconfig/, /var/, /netscaler/, ns.conf.
Full: Backs up the same data as a basic backup however captures additional files that are less frequently updated:
Folders and files that are backed up include /nsconfig/, /var/, Certificates, License Files.
For a full list of what is backed up see http://support.citrix.com/article/CTX200418.
Click Backup.
After a few moments the backup file will appear as below.
Clicking on the Action button allows you to download the backup file to local HDD or perform a restore using this backup file.
Backups are stored in /var/ns_sys_backup/ on NetScaler. 
To perform a backup using the CLI, run command create system bbackup “backupname” -level Basic/Full
You can specify Full or Basic and write a comment using the -comment switch.
The new backups are now within the backup directory.
The backups also show within the GUI.
Run show system backup using CLI to get a list of backup on NetScaler.
To restore NetScaler to a previous backup, run command restore system backup “backupname”.
Now run reboot -warm, this performs a warm reboot of the NetScaler at which stage the restore will execute.
You can also restore via the GUI. By default before a restore a backup is performed on the NetScaler. You can skip the backup by checking the Skip Backup box. Click Restore.
Navigate to System -> Reboot.
Check Warm reboot and click OK.
Backup and restore using Citrix Command Center.
Citrix Command Center downloads NetScaler configuration, licence files and SSL certificate files from each discovered NetScaler and stores these files in the CCC database. As a NetScaler device is discovered or a rediscovery takes place, backups of the discovered/rediscovered device are also performed. By default backups are performed every 12 hours and a maximum of 50 backups are stored within the database.
To edit the backup schedule and frequency, navigate to Administration -> Inventory Settings.
As you can see below the archive interval is every 12 hours and the numberr of previous backups to retain is 50. You also have the check box to enable archiving once a Save Config trap is received by Citrix Command Center from the NetScaler appliance.
To view backups of a NetScaler appliance, navigate to Citrix Network, click on your NetScaler and click Details.
A new window pops up and at the bottom you will get a list of all the current backups. The date, time, and comments section give additional information such as the backup was created at the scheduled time.
Select a backup file and click Download -> OK to save a backup to your local machine.
To perform a manual backup, click Backup Config -> OK.
After a few moments you will see the newly created backup. Notice the comments indicates the user requested this backup which is correct.
To restore a NetScaler using a backup created with Citrix Command Center select a backup file of your choice and select Restore Configuration.
Click OK. The restore takes place and you will have to restart NetScaler using GUI or CLI.
Backup and restore using NetScaler MAS (Management and Analytics System).
NetScaler MAS is the newest platform to automate, manage, orchestrate and monitor appliances such as the NetScaler. It is seen as the replacement to both Citrix Command Center and NetScaler Insight Center. As a result it can perform many of the functions that you were familiar with on CCC/NSIC. Navigate to System -> Instances Backup Settings.
For any instance adding to NetScaler MAS, a backup is by default going to be taken every 12 hours and a single copy will be kept. You have the otion to password protect all backups using a password of your choice. You also have the option to modify the backup interval. From what I believe, the maximum number of backup files to retain is 3 however this is not something I can confirm at this stage.
To view or create a backup of an instance, navigate to Infrastructure -> Instances and select of your NetScaler then click View Backup.
As yet, no automatic backups have been performed. To create one click Back Up.
Specify to password protect the file. If you had of specified a global password under System -> Instances Backup Settings you would have the option to use that. Click Continue.
The new backup has been successfully created.
To restore check the backup file and click Restore -> Yes.
Specify the backup password you used when creating the backup, click OK.
You get a nice GUI view of the restore progress plus the NetScaler is automatically restarted for you.
Note: Do not modify backup file names or modify the contents of the backup as it will invalidate the backup file and cause restores to fail.