Hi Yichen,
Gald you found the answer. For the benefit of those who don't understand what's going on, you can wrap images around text in the image editor itself:
The way the image is aligned will depend a lot on the theme you're using. If you're not satisfied with that, than you need to have a look at the Codex to see how to change the settings:
http://codex.wordpress.org/Wrapping_Text_Around_Images