Liferay Learning resources

Various resources which a person can use to learn Liferay

The best option is to go through the official documentation its available in multiple formats. Official documentation is a comprehensive resource for developers.
web / online - https://www.liferay.com/documentation/liferay-portal/6.2/user-guide
                      https://www.liferay.com/documentation/liferay-portal/6.2/development

print - http://www.lulu.com/shop/rich-sezov/using-liferay-portal-61/paperback/product-21014853.html

downloadable pdf  - new version pdf will be released soon

Liferay also offers trainings in different modules, person can enroll for these trainings as per their requirements.
I would recommend undergoing  Mastering Liferay fundamentals before taking on developing for Liferay platform course

https://www.liferay.com/services/training

There are many videos available on youtube, search with keyword + liferay
Video of Liferay web events along with slides are available at - https://www.liferay.com/events/web-events

If you are stuck with any issue or need expert help , community resources like wiki, blog forum are best place to seek pointers - https://www.liferay.com/community/welcome/dashboard

Books from independent authors are also available in print and ebook format.

Also join various active Liferay user group where people meet regularly and share their knowledge.