Single Account
If you only have one account then when you launch the app you just need to enter the account password; to sign in enter the account password and press return or tap the arrow button.
Multiple Accounts
If you have created more than one account then tap the account in the list.
After you have chosen the account enter the account password and press return or tap the arrow button.
Use the Switch account button to return to the account menu if you need to choose a different account.