Just stick your hand out the window next time you go flying and you'll get a good feel for how it works
If you have an "alpha" readout inside your cockpit (from the AoA vane), it's easy to see what's going on behind the scenes. But there are other ways to observe what's happening, other than looking at the vane on the wing it you can see it!
When in "level" flight, look at the AI (or just remember what you do) and note the difference between the waterline and horizon (attitude in degrees)......this is your AoA, or what the vane is reading (hi/low AoA). Then play with various flap settings/speeds and note the attitude and you'll see if you need to decrease or increase your AoA to maint level....as mentioned by the others.
On approach with.........
a TEF failure (LEF only if fitted or flapless) you'll need a higher AoA to create more lift and/or more speed. Remember your higher attitude flapless approaches whilst maintaining the same rwy aspect.
a LEF failure (TEF only) you'll have a lower AoA on approach and a fairly higher airspeed to have the same lift at the reduced AoA.