I’ve spent my entire career (nearly 40 years) as an automotive technical writer. For the most part, you can always trust a manual as being accurate. YouTube has a lot of good how-to videos – and a LOT of videos that are that are full of incorrect information and downright dangerous or stupid information!
If a manual does not have good illustrations and you want to see how something comes apart or goes together, then look at some videos on YouTube. If you need adjustment procedures or specifications, use (1) a factory service manual or go to the OEM technical information website for the specifics, or (2) a good aftermarket manual (Chilton, Motor or Mitchell) or an online information resource such as AlldataDIY.com or Michell1.com. The online resources do charge an access fee, but it is well worth the minimal expense to get the correct information.
There are also a number of free online automotive technical resources including AA1Car.com.
A lot of people also search online forums (including this one) for how-to and tech info. Forums can be an excellent resource, but they also contain a lot of misleading or totally incorrect information too. Sometime you are more confused than informed after researching a topic and finding dozens of conflicting answers!