I suggest that you give an example of what you have in mind. I can think of several possible approaches, and which is best will depend on details of your design and what you need to accomplish.
I have a portal on a layout, which has few rows. The portal has the create new records option allowed. in each portal I have 'start day' field and 'end date' field.
When i type a new record date, I want to compare the new record 'start date' to the previous row 'end date' so that the new start date is later than the previous end date.