Magenta 2 core problem or not

[Beginner234]

When I am writing a module to Magento 2 what should i do (front-end). 

• If I do not know how to locate the precise spot where the issue might be (related files / dependancy )? 
• How to make sure when the issues is in Magento 2 core code and when it is not?

[JLHC]

Topic moved to the Magento 2 section. 

[avstudnitz]

I recommend taking the Magento U online courses as a start which are free until January 31th. You can find them at https://u.magento.com/magento-2.

Of course, you can also take an on-site training or get into Magento 2 development by reading books and blog posts. Sorry, your question is much too generic for a more concrete answer.

[Beginner234]

Sorry I did not reply sooner. I try to ask again more specifically.

First of my questions was about issues which fall under Magento core problems. Meaning when it is justified to post to github Magento2 repository problem as Magento2 issue!

Second question was about tutorial which would narrow down the spot where issues would be located (I am posting it hire because it is programming related).

Two user case to explain better what I ask:

1. Shop owner updates his/her shop to new more secured version but something happens and the page does not work as expected. WHAT TO DO! (how to narrow down if it is some module or maybe it is theme issue?)
2. Second user case would be about programmer who writes code and gets error, but the error is too general to understand (why the code is not working? how to narrow down the reason). STEPS THAT DEVELOPER SHOULD TAKE BEFORE POSTING TO ANY FORUM!