Xumm allows developers and app users to "meet up".
While app users can simply use the Xumm application interact with the XRP Ledger with their accounts, balances and transactions, the true power of Xumm is unleashed through the platform available for developers.
This way users can interact with third party tools & platforms in the most secure and convenient way, while developers don't have to worry about wallet & key management.
XRP Ledger transactions are traditionally user initiated: users open their wallet, enter the destination, amount, etc. and then you submit a transaction. This is referred to as a Push Transaction.
In retail / e-commerce & third party interaction scenarios, the ideal flow is inverted: a Pull Transaction. The third party environment wants the user to sign a specific transaction, and a transaction to sign is offered to the user.
This is where the Xumm platform comes in. An XRP Ledger transaction template can be delivered to the end user through the Xumm platform. This is called a Sign Request.