With Marygold you can make transfers between any of your Marygold and/or other external (linked) bank accounts, but the user experience does vary a little depending on where the funds are moving from.
If you a making any payment from a non-Marygold account (e.g. your main current account at Barclays) then after you input your instruction us via the Marygold app (i.e. move £100 from your Barclays current account to a Money Pool account in Marygold) then Moneyhub will initiate an Open Banking payment request directly with your bank. As none of your current account login credential details is passed to Moneyhub (nor Marygold) you must authorise the instruction yourself within your bank app when prompted. Moneyhub is FCA authorised to initiate the transfer request and submit the detail to your bank (ie. amount, etc) but you must authorise the transaction.
If you are making a transfer from a Marygold Easy Access Savings account (e.g. from one of your money pools) then this instruction can be processed automatically by the account provider Griffin.