Important links for magento 2

1)    https://magecomp.com/blog/add-custom-file-upload-control-magento-2/  

2)    https://blog.landofcoder.com/magento-2-install-extension/

https://magenticians.com/create-custom-theme-magento-2/

http://unitedwebsoft.in/blog/complete-magento2-theme-development-html-to-magento2-theme/