When creating a Form Level rule there is an option to configure Pre-Actions. Pre-Actions allow you to run one or more action prior to the execution of the rule.
To best illustrate this, let's walk through a specific example.
In this example, we have we are going to set the field's background color based on the user's input. We've setup a List field with 5 answer options as shown below:
For anything that is considered high severity, we are going to set the color to Red. The following screenshot shows a Pre-Action the first Clears the field color, then a Rule Condition that will set the Color to Red if the Severity is Very High or High:
It is important to note that this same logic can be accomplished with an "Otherwise" or "Else" condition with your rule as shown below.
This often comes down to a matter of preference in rule setup.
Note: One important thing to note is that Pre-Actions run no matter how the rule conditions are setup, so if you aren't careful, you could easily cancel out the actions of another rule.