When a company is about to announce the dividend for their company’s share holders, Cum-Dividend And Ex-Dividend are then announced.
Let’s assume that Company A has announced Cum-Dividend And Ex-Dividend dates.
This is a time period in which, if a person buy shares of the Company A, then he/she will get the latest dividend. The Cum-Dividend is a time period like: five or so days.
This is the time period in which, if a person buy shares of the Company A, then he/she will not be eligible to get the latest dividend on shares.
If shares are bought in this time period, then the previous buyer will get the benefits [that is: the dividend].
What is the use or purpose of Ex-Dividend or Ex-Date?
Buyers who bought shares of the company in the Cum-Dividend time period, if they want to sell the shares and if they still want to get the Company A’s dividend: then in the Ex-Dividend time period, buyers can sell the shares and they will still get the dividend.