If you are new to Alteryx, tools such as the Input, Formula and Output will automatically display text in a white box underneath the icon in your workflow. These boxes are called annotations. You can enter your own text to briefly describe what functions the tool is performing on the Annotation tab.
Why customize these? Annotations are helpful if another user has to run your workflow and it will help them to understand your data flow. Documentation is always helpful if you were to win the lottery tomorrow and other users need to take over your processes.
Simply click on the tool in your workflow and select the Annotation icon in the left-hand side of the Configuration pane. You can enter a custom name in the Name field, place the annotation on the top of the tool instead of below it, and/or customize the text in the Annotation field.
In newer versions of Alteryx (after 2020.1) you can click F2 when a tool is selected to easily edit the annotation as discussed here. Also remember to keep your annotations short! Use the Comment Tool if you need to add lengthy descriptions.