Dividends are payments made by companies to shareholders as a portion of their profits.
If you hold dividend-paying assets in your investment account, these payments will be paid directly to the buying power no action needed on your part. You can then withdraw them from your investment account buying power to your nsave USD or GBP account.
Withholding taxes will depend on the your country of residence. You can see the info clearly in the Activities section of Invest. Simply click on the bell on the top right next to the search bar.