Yes, we reset the garage door opener with a youtube video. And completed many other tasks as well.
The battery in the keyfob to our car stopped working while we were on a hike in Canada, far from any place to buy a replacement battery. While we stood sweating outside the car and debating what to do, my son put down his phone, held the fob to the door, and unlocked it, then held it to the ignition button and started that too.
When the wooden slats on D’s IKEA bed kept sliding out of place (usually in the middle of the night. leaving her mattress and body on a slant), I found a number of fixes on Youtube–because apparently this happens ALL THE TIME with IKEA beds (grrr IKEA). I kept plowing through them until I found one that didn’t require tool skills, posted by a dad who clearly was as averse to using a drill as I was. The solution was heavy duty Velcro, and three months later, so far so good. (I’m pretty convinced the universe runs on Velcro, and this belief was confirmed when I watched videos of life on the International Space Station, which could not function without Velcro.)
A bit off topic, because I haven’t put any of my learning into actual practice (and probably never will), but lately I’ve been fascinated by Youtube makeup tutorials, especially the ones where the demonstrator uses a dizzying number and variety of products: toner, moisturizer, sunscreen, primer (one for face, one for eyelids of course), eyebrow pencil or powder or both, multiple shades of eyeshadow from a pricey palette applied with multiple styles of brushes, eyeliner, mascara, foundation, concealer, blush, contour, highlight, finishing powder (each of the last six applied with a dedicated brush or blender or both), lip liner, lipstick. The “afters” always look like completely different people from the “befores” (and not necessarily better). I find the videos simultaneously mesmerizing and hilarious and have to wonder whether these women ever make it out of the house before noon. (I think this may be one more thing we can blame on Kim Kardashian.) I’m considering posting my own how-to video, where I slap on some sunscreen, more or less cover the dark circles under my eyes with concealer, swoop a little blush on my cheeks to avoid that corpse-like look, add a swipe of whatever lipstick rises to the top of the makeup bag, then studiously avoid mirrors all day.
We ordered a new fridge and stove on line from our local Lowes (we live outside of city limits and save almost 5% sales tax not ordering it in store). They were supposed to contact us for a delivery time but showed up the next day. We sedentary - I was going to have them come back but H told them to leave them on the back porch (sigh). When we came to move the large French door fridge into the house we discovered it wouldn’t fit through the doors. Found a you tube video that walked us through removing the 2 doors and 2 drawer fronts and putting them back after getting them into the house. (But told H we are NEVER doing anything like that ourselves again).
Bought a luggage strap i couldn’t figure out how to put on case - you tube to the rescue.
Replaced monitor on my netbook – $14 part, saved $100 in labor.
Fixed dishwasher clog, took apart dishwasher and reassembled it with no extra pieces – a miracle!
Many, many quilting videos, in particular joining the ends of binding on a quilt.
mathmom, that How to Fold a T-Shirt youtube is the greatest! Thanks for posting.
H fixed the washer that wouldn’t open or spin and had a load of laundry in it; also fixed a “whistling” toilet; Computer issues; How to trim our plum tree; And I learned a lot about how to use my Instapot for various recipes…
Inspired by this thread I went looking for packing tips for my upcoming trip - I will be gone for 3 weeks and 2 of them my brother and I will be in Zambia and Zimbabwe and staying in 4 different hotels. I’ve been fretting about what to pack, how much to pack etc. I want to pack light as far as possible but it is winter there and can be cold at night so need a variety of clothes.
Found some great videos for folding and packing. I can’t believe I’ve got to 65 and never learned the ranger method of folding my undies! And it works with jeans etc. - so easy. Now I can fit 2 weeks of knickers into a large zip lock bag i may even take undies for the whole 14 days and not worry about trying to wash them.
So thanks for starting the thread!
Also not educational, but I’m mesmerized by tornado videos on YouTube, even though tornadoes terrify me and have been the subject of nightmares for most of my life.
There is one filmed by a man who filmed a tornado approaching his home. He never moved away from the window, even when it hit his house. He survived, but his wife, who was downstairs, did not.
I must be the only person who has limited youtube experience! I do follow one of those make up/skin care people who posts twice a week but, otherwise, I need to change my ways and check it out more often. I’m very impressed with all of you.
Two dizzying youtube videos convinced me that I could a) fix the washer myself, and b) would much rather pay the appliance repair person to do that job for me. 
Along those same lines as @happymomof1, the videos of how to change your iPhone battery convinced me I am happy to have Apple change it for me, especially now that they’ve reduced the price to $29 instead of $79, for 2018. Yes, I COULD change the battery but I may also damage it and render the phone useless. 1st world problems, I know.
I do admire folks who DO use the videos to fix all sorts of things. If things are very involved, I’m happy to pay the right person to do the repair.
My DD’s farrier once joked that his DS has learned many things from YouTube and after receiving his driver’s permit confidently, DS declared that he wouldn’t be needing a driving instructor because he could learn how to drive by watching YouTube videos.
The farrier followed up by suggesting that my DD’s horse might benefit from watching a YouTube video of horses standing nicely while being shod. 
;))
I watched a few dog training videos - I do clicker training and I’ve gotten some extra help watching them. Also attempting to teach my dog to roll over and play dead and they show step by step how to get the dog to do that.
I’m trying to program my hunter douglas blinds on the app. I just found a youtube for that too.
I learn excel functions as well. It helps me to actually see what someone does vs reading instructions.
I just learned a new word today:
farrier
Never heard that word used ever.
I check the youtube video every single time I clean my Anderson tilt-in windows. Maybe I could remember how to do it if I cleaned them more often than every six months
How to make a corsage. Made prom a whole lot cheaper!
Oh - how to repair a hole in fiberglass when you only have access to the outside and can’t reach the inside of the hull. Very helpful.
Oh yes, viewed some quilting videos and was able to make quilts for my kids decades ago. Mine don’t look anything like theirs but we’re treasured anyway.
We replaced the engage blade lever on the lawnmower with help from youtube.
DH learned to replace a broken brick on the fireplace hearth, and how to replace a garbage disposal.