A "Droplet" is basically a server instance. To create a new one, click on "Create A Droplet":

Then you'll need to provide some information about it.

Droplet Hostname: A "hostname" is up first and isn't super important - this is the name of your Droplet so you can identify it if you have a few. Don't use any spaces or special characters/symbols.

Select Your Size: There are 6 size options, but the smallest 512MB should be plenty for the majority of blogs. If you run out of resources, you can always upgrade later.

Select Region: Choose the region closest to you or wherever you want your blog to be the fastest (for your intended audience).

This is the important part!

Select Image: Under 'Select Image' > 'Applications' > 'Ghost on Ubuntu 12.04' and select a "Enable Backups" under settings.

Digital Ocean will then confirm that it's happening: