If you have a blog from WordPress.com and need a backup, then follow these steps:
1. After login to your blog, click My Dashboard.
2. Click Tools, then choose Export.
3. Click Download Export File to save all data to your computer.
When you need to use a backup file (in XML format) on another WordPress blog, go to step 2 and choose Import function instead. Moreover, you can also import from other systems (Blogger, LiveJournal, etc.).
Backup your blog before it’s gone!