This seems to be a recurring topic in my comment trail so I want to mention it briefly.
I like http://www.blogger.com/ because it's easy.
Setup and Getting Started
1) Create an account. (you may or may not need a parent's help)
2) Pick the style and color you want
3) Go to Layout and drag the squares into the position you want if you want anything different than the default. In layout you can add video players, follower modules and other add-on items like games and ads.
4) When ready start click on the Posting tab, add your title and start writing. Use the toolbar on the posting area to add pictures and video. When you're done, click publish post.
5) To moderate comments... Click on Post, then on the Comment Moderation link and approve the comments you find acceptable.
What Your Blog Should be About
Wizard101 wants original content and some significant amount of posts before they'll add your blog to their site. Original content simply means that they want to hear what's important to you. What they DON'T want is the same content as someone else. So resist the temptation to post about the same things others do.
Write every day if you can so you build content quickly and so you have something new for your readers. Lastly, post comments on others blogs so they'll return the favor and visit yours.