You can use the Instructions for User field setting to provide additional context or instructions for filling out a particular field in your form. When someone clicks into a field to fill it out, the instructions for that field will appear in a box to the right. They'll disappear when they move on to the next field, so you can provide necessary context for each field without cluttering your form.
You can apply this setting to any field type.
To add instructional text to a field: