If you want to export your contacts into a CSV file, it's very easy to do.
Navigate to the Contacts tab
Select the checkbox to the left of the name column and all contacts will be selected. To select a specific number of contacts, select the prompt in the green bar that appears.
Select the Actions dropdown and then Export Contacts
In the pop-up window, click Export Contacts to begin the download
Your file will be downloaded as a CSV
This type of Export will include:
First and Last Name
Account Company ID
Phone Number & Type
Email Address & Type
Physical Address & Type
Assigned Sales Rep
This Export will NOT include:
Contact Time Zone
For a FULL database back-up, see this article.