An incoming link is a link from another website that hyper links to your site mentioning one of your keywords. So for example if your blog was about dog training and another site said "see this blog for dog training tips" and the words "dog training" were hyper linked to your site then that would be an incoming link.
All major search engines rank your site or blog more favourably the more incoming links you have. You can create an incoming link (or backlink as they are called) here on hub pages. Simply create a hub on any subject related to your blog and blend in a couple of related keywords that you will then hyper link using your blog url. After doing this a few times and getting a variety of backlinks from different sites you will see your search engine rankings start to increase. As you climb the search engine ranks your traffic will also increase.
Its also worth mentioning that getting backlinks is just part of getting high search engine rankings, you must also make sure that your content is good and that your site or blog is search engine friendly. Copied content, poor quality content or content that has too many repeated keywords will count against you, but if you have a good site then building backlinks should be your next priority to gaining good rankings in the search engines.