Quick question.

An ILS is composed of a localizer (LOC) and a glide slope (G/S).

One you intercept the localizer and two you catch the glide slope.

Button LOC is localizer only.

Button APPR is for both.

The LOC can be use on a LOC only approach or on an ILS approach. But on ILS the APPR button is better.

In some cases, you can intercet the LOC only, keep on descending, and then activate APPR to catch the glide slope.

APPR+AP1+AP2+RADIO 50 or 100 for autoland.

Generally:

LOC* FLAPS 1

G/S* FLAPS 2

2000 FT GEAR DN FLAPS 3/FULL in a row.

A320 What About Arming Conditions of APPR Modes - YouTube