You open the transfer window by clicking on the Stake button on the dApp you wish to support. You can select what funds you would like to use, funds that are transferable and in your wallet, or use it from another dApp you are staking on. In this case, I want to transfer some funds from Stake Technologies to the Community Rewards program. Enter the amount you wish to transfer (in the case of Shiden, the minimum is 50 SDN) and click on Stake. At the end of the process, you finalize by signing the transaction.