Deep Dive: Prepare Pipeline
The Prepare page has the options for transforming the raw data into report-friendly formats. The pipeline at the bottom of the page shows the history of these transformations. The pipeline itself has useful tools for managing the transforms, including:
Add Step
Add Step is the node at the end of the pipeline. Add Step adds another transform in the pipeline. Adding a step will add the transformation as the last step in the pipeline. For information on adding steps between existing transforms, see section Insert Transformation Before.
Cancel
If you are adding atransform, you can click the X icon to cancel the action. This will close the Transforms page and your list of sources will be visible again.
Descriptions
Users can add a description to a transform in the pipleine. Click on a node to open its menu and select Description.
Hovering over a node will display the user who created it and when along with the node's description.
Edit
If you need to edit an existing transformation, click on a node to open its menu and select Edit.
Insert Transformation Before
In some cases, the order of your transforms is important. You may need to insert a transform before an existing transform.
For example, you may have merged two columns and then discover you need to fill in some empty values in one of them. It makes sense to take care of the null handling before doing the merge.
Click on the transform you would like to add the new transformation before and select Insert Transformation Before. 
Delete
To delete a transform, click on its node to open its menu and select Delete. You will then need to confirm your deletion by clicking Apply. 
Note: A Prepared source that has dependent transformations cannot be deleted until those dependencies are removed. Examples of dependent transformations that may rely on a prepared source include Merge, Append, Lookup, or Custom Transform.