How to identify a problem on your device?

@ofir89 that is a lot of questions. Let’s start with a few answers:

1. How to identify the problem (There is a special guide that explains all the symptoms that may happen on a mobile device and the solution?)
2. No guide. You are your own guide. You will have to learn what part of the circuit has what function and diagnose a failure based on that. Time to learn how to read schematics :-)
3. How to open the device correctly
4. That will depend on what phone you have. Some are similar most are different. That is where a site like iFixit comes in handy. There are plenty of guides and teardowns available that will help. You will always come across a phone that you have never worked on, so you have to experiment a lot (oh yes, you will also learn that you are going to break things;-)
5. How to correctly output and return a flat cable
6. Not sure what you mean by that. you can see the placement for some phones by following the guides and teardowns either on iFixit or Youtube etc.
7. Is there an online guide that explains and shows all the components and components on the motherboard and plastics?
8. Nope. You will have to learn to identify those. Schematics for some phones are available (costly) but in general you will have to depend on your knowledge or the knowledge of people on here. There are experts like @refectio @teetopp @benjamen50 that are always willing to help out.
9. Is there a good guide that explains in general how to replace screen and glass with popular devices? Only the aforementioned guides from iFixit and some scattered once on Youtube etc.
10. Where to buy spare parts for phones? That will depend on where you live. Stay away from places like ebay and ask other techs where they buy their parts from. Establishing a good relationship with a seller will help you to make sure you get good reliable parts.