There are a few sites which I found useful to a SharePoint Developer.
http://microsoftsharepointsupport.blogspot.ca/
http://microsoftsharepointsupport.blogspot.ca/2015/05/understanding-sharepoint-apps.html
Apps series
http://www.sharepointnutsandbolts.com/2012/08/sharepoint-2013-appsarchitecture.html
Microsoft SharePoint Online Management and Control
http://microsoftsharepointsupport.blogspot.ca/
http://microsoftsharepointsupport.blogspot.ca/2015/05/understanding-sharepoint-apps.html
Apps series
http://www.sharepointnutsandbolts.com/2012/08/sharepoint-2013-appsarchitecture.html
Microsoft SharePoint Online Management and Control
https://www.youtube.com/watch?v=4oILqaF3GTI
SharePoint 2013 - JSOM and Rest code screen shots
https://onedrive.live.com/?id=70CB108637597235%21310&cid=70CB108637597235&group=0
SharePoint 2013 - JSOM and Rest code screen shots
https://onedrive.live.com/?id=70CB108637597235%21310&cid=70CB108637597235&group=0