Bike gearing

The shifter on the left controls the front derailleur and the right shift controls the rear. Once you’re used to the bike, you won’t be looking at the indicators. Keep your front derailleur in the middle gear for most riding, shifting to the small ring when you’re pedaling up hill, and shifting to the big ring when your on flat ground or downhill when you need/want more speed. The rear derailleur will see the most action and the exact gear Is less important that maintaining a good cadence for yourself. All this being said, the Red line in your rear shifter is the indicator but if it’s not moving it may be broken. Your front shifter appears to be broken because there’s no visible indicator