Hi Yuto...
To post images and URLs, just click the button at the bottom of the post box (under UBB code). These will bring up a box where you can enter the URL. For a URL, enter the web address and then the text you want to use as a link, and for a image enter the address of the image.
To make a banner you need some kind of program like Photoshop, PaintShop Pro or even MS Paint will work. You can then insert images and text to make a banner.
As for Dear Alf fanart, I'm not sure how long it would take. I don't even know if they use every fan art that they recieve, or if they get a lot, there might be a bit of a wait.
Hope that's of some help!
Abe Babe...