http://www.shellblack.com/whiteboard/overview-of-leads-account-and-contacts-the-salesforce-data-model/
https://trailhead.salesforce.com/en/module/admin_intro_accounts_contacts
I should do the trails (other than developer and admin) to get basic idea of how Salesforce work.
https://www.youtube.com/watch?v=Ta0qvfOYPSI
https://www.youtube.com/playlist?list=PL9ooVrP1hQOHd5nCn2r6bTptxmC95gYns - downloaded
https://www.youtube.com/playlist?list=PLdYQMTciVWO9xjvh1J7SXjhzpnzWvLih4 - downloaded
https://www.youtube.com/playlist?list=PLEiEAq2VkUUK0x8URvIzHZ3_JYTdHxTAd - downloaded
https://www.youtube.com/playlist?list=PLlnOmrO1a2caCp04HjUAqFNeMo7fZd1-u - downaloded
https://www.youtube.com/playlist?list=PLYFO4h1fAA0pZxKjkTxptlcW6mh1CDi1- - downloaded
https://developer.salesforce.com/trailhead/module/starting_force_com
https://developer.salesforce.com/trailhead/module/visualforce_fundamentals