Yep L indicates the low speed / idle mixture screw.
After you've got the idle set, it's time to adjust the high-speed mixture (H screw). Up to a certain point, the engine burns cleaner and makes more power as you lean it out, but if you lean it out too much then the engine will rev too fast and combustion temperatures will get too high, very possibly destroying the motor in short order. Adjusting the high speed without a tachometer depends on your ability to hear a particular sort of rhythm in the sound the engine makes. The rhythm you're listening for, commonly called "four stroking," should occur when running the saw at full throttle with no load, i.e. spinning the chain in the air, not cutting any wood. The rhythm exists in this situation because the engine is getting a little more fuel than it can use and is not actually firing on some revolutions, resulting in a sound that's something like the sound of a single cylinder four-cycle engine (i.e. most lawnmowers). You want to gradually adjust the H screw until you find a setting where it "four-strokes" at full throttle with no load, but just barely "cleans up" or stops "four stroking" under load, i.e when making a normal cut. If it four strokes under load, then it's set too rich. If it doesn't even four-stroke when not under load then it's too lean. This is a fine adjustment; don't expect to find the sweet spot by turning the screw 180 degrees at a time.
The big challenge with tuning by ear is learning to recognize that sound. Videos and recordings don't always have the greatest audio quality, and don't always make it clear what you're listening for, so this is how I've tried to describe it. I'm just copying this from an answer I gave to a similar question elsewhere:
First, try making a sustained "Z" sound, as if you're imitating a bee's buzzing: Zzzzzzzzzzzzzzzz. Got that far? Okay, now while you're doing that, try pulling the tip of your tongue back away from your front teeth, along the roof of your mouth until the tip of your tongue starts to flutter and make a sound more like a rapid D D D D D D D D D, very similar to a rolled R, made up a series of distinct beats as your tongue repeatedly hits the roof of your mouth.
Four-stroking is like the latter sound, the D D D D D D D, and that's what you want to hear when the engine is running but not cutting anything. The ZZZZZZZZZZZ sound, smooth with no staccato beat to it, is the absence of four-stroking, and that's what you want to hear when you begin a heavy cut. It should switch back and forth between the two, from ZZZZZZZZ in the cut, and then back to D D D D D D D D when you ease up the pressure and the engine doesn't have to work so hard; this is what people are referring to when they say a saw should "clean up in the cut." If it sounds like ZZZZZZZZZZ even when it's not working hard then you're running lean and courting a scored piston. If it sounds like D D D D D D D D even when working hard then you're wasting fuel and performance isn't what it should be.