marshmallow twrp and root help

just installed 6.0 on my lg g3 d855 32gb
trying to root and install a custom recovery but not able to. used the method with kingroot then installing supersu from twrp but then when booted supersu keeps asking to update binary and then freezes. am using the v30b-global-com version
any straight forward way to do it? without kingroot
i dunno if that’s weird, but i can’t even enter the fastboot to install the recovery using fastboot command