Whatfore the LOC button is than???

And what does it mean in manual than?

"When pushed, the LOC switch arms the AFDS to capture and fly the localizer front course. The switch must be pushed prior to localizer capture.
LOC is displayed in white on each ADI prior to capture.
The localizer will not capture if the intercept angle is greater than 120 degrees or 2.5 NM.
The current lateral nav mode (LNAV, heading select, or heading hold) remains engaged until localizer capture.
"