Hi! There are two ways:
1.) Unofficial blogs. I've seen several of these, and you basically make a post about whatever you want, but then add the "____'s blog" at the end of the title.
2.) Official blogs. You have to ask KT personally, and you must have a certain amount of points to get one. I believe it's 10,000 points? Anyways, they'll ask you what you'd like it to be named, and then BOOM! They'll create it and you've got your own little corner of the internet!
Hope this helped!