Custom designed sites
I keep backups of all custom designed sites so you don't need to worry about this. Backups are stored locally and I am working towards setting up a backup facility online, which each customer will have access to.
In the meantime you can request a copy of your website at any time.
Joomla CMS sites
It's especially important to make regular backups of a CMS site, and you should run a backup whenever you make any changes to the website content.
To make a backup of your website go to Akeeba Backup for Joomla - Control Panel under Components:
Click the Default Backup Profile under One-click Backup:
A progress page will appear.
IMPORTANT: wait for the completion message. You can then navigate away by clicking the Control Panel button.
By default three backups are stored on the server and older backups are deleted automatically.
You can download backups from the Manage Backups section. Akeeba will warn that it is safer to use FTP to download the backup but in practice this should work fine.