How do I unlock this phone?

[rickharrison47]

*** TAMPERED ***
*** LOCKED ***
A11_UL PVT SHIP S-ON
HBOOT-3.19.0.0000
RADIO-1.101.1372.19.0921
OpenDSP-v28.2.2.00546.0331
OS-1.11.506.8
eMMC-boot 1024MB
Sep 21 2015, 21:46:28.0

FASTBOOT AC

<VOL UP> to previous item
<VOL DOWN> to next item
<POWER> to select item

HBOOT
RAMDUMP
REBOOT
REBOOT FASTBOOT
POWER DOWN

My friend is selling me his old android, however, I'm not sure how to unlock this phone to use. If anyone can help that would be appreciated!

 

[Rukbat]

You don't, he brings it to his carrier and asks for it to be unlocked. Then you buy it.