Adobe doesn't provide a standard dummy Adobe Analytics data set with partner sandboxes. Partners will need to create data in their Adobe Analytics instances if they want to test their integrations with data.
How you bring the data into Adobe Analytics depends on how you’re going to use it. If you just want to test data export methods without worrying too much about how realistic and accurate the data you’re exporting is, then the Data Insertion API or Data Sources may be the easiest way to do it. Click on those links above for explanations of what each of those features are and how they each work.
If you want something a little more realistic, then tagging a few pages of your own site or a test site is probably your best bet. If you can, use Adobe Experience Platform Launch (Adobe's tag manager) to tag your site.
Basic implementation of Adobe Analytics through Adobe Experience Platform Launch
Adobe Experience Platform Launch is the new tag management system from Adobe and is the way that most new clients will deploy Adobe Analytics on their sites. This video gives an introduction to the tool and this getting started guide has instructions for deploying Experience Platform Launch on your site. Install the Adobe Analytics extension in Experience Platform Launch and configure it using the default settings where possible.
Basic implementation via other methods
This help doc has instructions for non-Experience Platform Launch implementations and links to resources you can use. I don’t recommend using these methods—they are all more complicated to use than the Experience Platform Launch method, but they are available if Experience Platform Launch doesn’t work for you.
Understanding Adobe Analytics
If you haven’t already, you should also refer to this Getting Started doc which walks you through the Adobe Analytics interface and help you set up custom variables and manage your users. Adobe Analytics is a pretty complicated product, so it can take some time to familiarize yourself with its interface.