To see how much EOS you have accumulated in dividends, check the section at the bottom of the dApp's window. Under it, you'll find a list of all the recent transactions involving your account. This includes the dividends that were accrued to you from transactions carried out by other users (see here to learn more about dividends).
You can manage your dividends through the Dividends Actions widget:
1) Reinvest – this means converting your dividends (in EOS) into POW to increase your stake. This way, you'll receive more dividend rewards from each transaction on the platform, because your share in the circulating POW supply will increase.
2) Withdraw - you can withdraw their dividends any time, as long as the amount exceeds the minimum threshold. Please note there are no automated withdrawals. 