You must REGISTER and LOGIN before you can place the ad.
(Do it now to save frustration later)

Pick "View All Categories" from the menu on the left.

Scroll down the list until you find the category that you want.
Click on it.

" Place an Ad In This Category " <-- look for this at the page bottom.
Then click on it to begin your ad in that category.

Choose and ad "type" (ie; For Sale, Item Wanted, etc. . . )
You will find the "Choose a Category" on the next page already is selected for you.

The rest is up to you to experiment with.
You can always go back and edit your ad at a later time through the "User Control" panel.

Uploading Photos:
We recommend that photos be shrunk to 640 x 480
A freeware program that does that is available here: visualizer_photo_resize.zip

Other useful information:

User Profile
This is a powerful selling tool.  The "User Profile" is a mini-website. 
It is found in the User Control Panel under "My Account"