Go to Superset and choose Data -> Datasets and click on the + Dataset button in the top right corner.
Fill in the Add dataset modal as follows:
Database: Choose the connection that you created above
Schema: Select druid
Table: Choose the table that you want to query from the dropdown menu. This dropdown menu should show the same datasets that are displayed in your RIll workspace. Each dataset represents a table.
Click Add
Now that you've created a dataset, you can click on it under Datasets and edit it (under Actions, over on the right) to configure column properties such as whether the column is a metric or dimension or whether it is your time column. See Superset documentation on Creating Your First Dashboard for more details.
Go to Superset and choose Charts and then click on the + Chart button in the top right corner.
Choose the dataset you just created. Alternately, when viewing the list of Datasets, you can click on the dataset name to create a chart.
You should now see the fields from your table in the Superset Explore menu and you can create charts as describe in the Superset documentation for Creating Your First Dashboard