Note that currently, you need to be an Admin to export. See this article for more information on making users Admins.
There are several ways you can export your data from Propeller. The most common way is to export the list you are currently viewing. To do that, click on the Gear icon and then Export to CSV:
You have the option of exporting related notes and tasks:
After you click export, you will get an email with a link to download the exported data. This will contain all the data according to the columns displayed and the filters applied.
Note that if you have a very large list, it may take some time to prepare your data.
If you want to export your entire database, you can select the Export All Data command.
This will create zip file that contains a CSV file for every main type of object (Accounts, Contacts, Opportunities, etc.)