How to make UART-UART cable
A summary of @jdv and @DoxyLover's answer-as-a-comment:

UART(ADAPTER) : UART (A13)
    ground(-) : ground(-)
           RX : TX
           TX : RX


and no connection of either plus(+) pin: those are for powering the device, and since the OLinuXino has its own power, connecting the plus(+) pins could cause problems if the voltages are different.