What are good links for SEO?

What is a hreflang tag?

I am have a query about regarding reselling product's content. In this case of reselling the product should I build content on my own and rewrite the original description in my own way. Or, should I just copy the content from the original page of the product. Which one should help me rank in Google better?

This might be hilarious to all the webmasters present here in this forum. But I would like to share some of my experiences with facebook recently. I started a campaign to get likes on my business page on facebook. Firstly, I invested about $10 just to test and I got back about 180 likes. So, in order to increase the rate I invested more at the second time it was about $20 and then I got about 300 likes. And on the third time when I increased the budget money again by $10 I got about 400 likes and not to mention the comments & shares are also varying very fast. Have guys noticed this kind of behavior of facebook?

What do you mean by Flux in SEO?

Are Paid Ads going to go extinct?? The evolution of search engines and the constantly increase in use of the services like adblocker. What do you guys say?

Where I can learn about email marketing? I am looking for any kind of a guide.

Can anybody provide me a good list of web 2.0 sites?

How to get more back links on a website?

Describe on page SEO techniques??