(a) Why is it important to market yourself?
It is particularly important today, in the age of the internet, to market yourself, because you are in constant competition with a huge number of applicants for a job. Especially for me as an prospective journalist it is extremely important to move around the Net. Let us just imagine that I would apply for a job as an editor in a news desk. My potential employer will certainly research about me and the other applicants on the internet. If I would not have at least a blog with some journalistic texts on the net, I would have very poor prospects to get the job as an editor. And not only because I have no texts online but also because the potential employer could think that I am not very internet-oriented.
(b) How can you build your brand online?
The first rule to build your own brand online is to create a strong recognition factor of yourself. In other words: Use the same profile picture for all of your websites/Blogs/Social-Media-Sites. You could also use similar colors for the website- or blog-designs.
The second important thing to build your own brand is to connect all of your sites on the internet with each other. For instance when you just have published a new text on your blog you have the opportunity to share it with your friends on facebook. When one of your friends on facebook works at a news desk, he could be probably your next employer.
It could be also important to "google" yourself regularly. Then you can see, what other see, when they google your name. In other words: If you find something about yourself on google, what turns you into an adversarial matter, you can try to get it "out of the net".