You can learn the fundamentals online. But you'll have to put in stick time to get good, and that means lots of sputtering and stuttering and stalling. But that's part of the game. just avoid any 4th to 1st downshifts on the highway, and you'll be fine.
I only drove a stick a few times before getting my Corolla, and I sucked. I also stuck it into 2nd a couple of times while trying to shift from 5th to 4th. So, the learning's part of the game.
I would suggest leaving downshifting to a later date. Upshifts and proper clutch actuation are tough enough as is when starting out. Take it easy on the gas. You don't need more than 2000rpm to launch in most cars. The key is finding the release point on the clutch. You want to push it in all the way, and (with the car in gear), release it gently until you feel a bit of resistance. Then you release it even slower until you can feel the rpms just start to drop from the resistance, then start feathering in some gas. Do this in a parking lot in first gear. Don't hold the clutch in forever or anything. But once you get an idea of where the clutch will start engaging the gear, you can practice over and over trying to see how much gas you need to apply and how fast, in order to start the car rolling. Once you get the car rolling, you can let the clutch out faster. Too fast and the car will bog, too slow and you're just wearing out the clutch. The same for applying the gas. You basically let off the clutch as you give it more gas. A see-saw if you will. One end goes up, the other down. You'll get a good feel for a comfortable launch.
Once you get that, find an empty hill and go on the incline and stop. With foot firmly on the brake, engage the clutch and put the car in first. Release the clutch until you feel it "biting" again, and then quickly, but carefully, move the foot from from the brake to the gas and apply maybe half-throttle, or roughly twice what you might have felt was comfortable for launching on the flat. Remember to keep the revs up in case you need more speed. For hills, overdoing it is better than the other way around. You can slow down quickly going up a hill, but not the other way around. If you spin the tires a few times, that's not a big deal, you'll get the feel of the pedal soon enough.
If I didn't say it already, take it easy for like the first week of learning. Besides hills, you don't need to launch at high revs. Shifting to 2nd and 3rd and 4th near redline is perfectly fine, but you don't really want to do it at launch. At launch, you're trying to move a huge ton of weight, so a lot of force is sent through the drivetrain to get the car moving initially, and higher rpms mean higher wear and tear and failure. But once you're at speed, rpms don't really screw up the drivetrain, just burns gas.
As for slowing to a light or taking a hill, you can put the car in neutral and coast. If you're in 4th, just shift to neutral and apply the brakes. It doesn't matter in a FWD car since the drive wheels are up front and have all the weight and traction. The balance of the car won't be upset any appreciable amount. Nothing bad will happen. It'll use less gas and put less wear and tear on the tranny. It's not exactly fancy, and it won't sound as good as a nice, crisp downshift, but that's fine. Once the car is slowed, you can choose a gear (based on the speed range the manufacturer lists for each gear) and try and get the rpms to a level that you think that gear would need for that speed. In other words, if you're slowing to 30mph, and you look in your owners manual and see that 2nd gear goes from 20-40mph at a redline of 5000rpms, then you'll want to probably rev the engine to about 3000rpms, engage the clutch (before or after revving, I don't think matters much), put it in 2nd and then release the clutch. You can probably see how this is difficult if you try braking as well, which is why you hear racing drivers talking about "heel-toeing" which allows them to use all three pedals at once. But that's why I say forget about downshifting for now. I couldn't heel-toe for a year and got by just fine with the slower approach.
Lastly, how you grip the shifter is overlooked too often. Place the knob in the palm of your hand. It's amazing how much smoother the motion is when you're hand is on top compared to the sides. Once you get good at driving, you can go back to a pistol grip or some variation of that. I palm mine now, but hold it with my fingertips when I'm pushing hard sometimes. I'm hoping to find a nice 8-ball shift knob soon as that would be perfect. PEACE.
