It depends on what type of text field you are using. A standard text field is limited to 100 characters. A long text field, by default, allows 3500 characters (although you can change the max number of characters).
If you need to provide instructions that exceed 100 characters for a standard text field, you might consider adding a long text field called "Directions," which only purpose is to provide instructions for other fields. We don't currently have a label field type for dynamic applications, but this would be a reasonable way to address that.