Some of the hosts offer back up some don't. I wouldn't relay on hosting provider. I would prefer to back up all my sites. The way how to do it will depend on your website and server type. I have cPanel where I can export all the database content and then I use FTP to copy all the files. How often it depends on the website. If you do not have new content one back up is enough if you have hundreds of products or comments or articles it should be done daily. It shouldn't take too long and it is not that difficult.