I have been asked few times, how to learn Sitecore and what are good references?
Theses are the approaches I recommend:
1- If you are absolutely new to Sitecore, ask your colleagues to show you Sitecore dashboard and Sitecore in general. Try to understand it from content editors perspective. You need to fully understand how your end users will use Sitecore to be able to design and implement new features for Sitecore.
2- Install Sitecore Habitat on your local computer as your reference and read through the Helix documentations
4- Sitecore has e-learning site which has free course for developers. You definitely can benefit from it.
5- You can read through Sitecore documentations based on the subject or module that you are interested to know more about it.
6- Sitecore Stack Exchange is the place you can ask your question and seek for help
7- There is Slack channel to meet other Sitecore devs and exchange knowledge
8- There is a facebook user group page which you can see latest blog posts related to Sitecore
9- Don't forget to attend Sitecore user group meetups in your Area, I'm helping with Sydney Sitecore meetup and will be absolutely happy to see you there. I have a blog post which I explained in details the benefits of attending the meetup.
10- Follow and read Sitecore experts blog posts. The blog post might not be related to you now but sooner or later you will encounter the same issue ;)!
11- Reverse engineering is another fun way to learn which I highly recommend it. Install ReSharper dotPeek or any other decompiler tool that you are comfortable with. Start looking into the Sitecore code and try to get inspired.
12- There are few Sitecore books that you can buy and read them.
13- Sitecore youtube video channel another way of learning sitecore.