1) Why is it important to market yourself?

I feel quite sure that it is important to market yourself for several reasons:

First of all, we are in a world leading by profit. Companies only want to hire the best people. So even you are not good you have to market yourself.

Secondly, even when you are in a company it is still good to market yourself because if you do it well, you will gain some credibility, you may also be identified by other firms, be hire, and maybe gain a better wage or a more attractive job...

2) How can you build your brand online?

When you create a product or you already have one it is often usefull to build your brand online. All the social media (facebook, blogs,...) are there to help you and it will cost less money.

But more and more companies know that and become on the social media. So you have not just to be present on it but also be different. As i see it, you can do contests, shock with ideas, videos or photos...