Absolutely NO ONE on here started as a "know it all", we all started as newbies, anyone who says they knew it all when they started, is either a liar or a BS'er, (or both).
I would venture to say that 95% on here are helpful & fairly nice, you'll meet the grumps no matter where you go or what you do, I just ignore them.
As far as the "smart alecks" making fun of your backing ability, I doubt they did any better when they first started, in general though, I think you'll find more of us out there that are ready & willing to help you learn, whether , guiding you back, or actually doing it for you, when you become super frustrated & your face turns beet red.
As far as fixing the engine of your truck, not everyone is mechanically inclined, I can get by, have pulled many engines, rebuilt some, replaced almost every part on an engine, but with the electronics on todays engines, I don't even try.
The main point is, don't be afraid to ask, thank the helpful, ignore rude, smart alecks. ;)