As always, the first step is to make sure that you are signed into the account you wish to use for posting. :)

The second step is to find the forum you wish to post it in and hit the new thread button.

You'll be presented with the Post screen:

Below the post screen, you'll note two options. One is for uploading images, the other files.

 You'll want, and we'll be dealing with the upper selection--Select Image file to Attach. 

Click on the Browse button beside the empty text feild. Clicking on browse will bring up a window that you can search your computer to select the image you wish to include in your post. Remember: Your image can be no larger than 500 pixels wide and 500 high, and must not be any larger in KB than 512 KB!

 Once you have located the image file you wish to include in your post, you may choose to either finish your post and hit Submit, which will put the image at the very bottom. OR, you may wish to place the image in a specific spot within the post. 

To have the image appear where you want in the post, find the img button.

Click anywhere on the text feild within your post and then click to img button. You will see this tag appear:

That means, the image you have attached to the post will appear there after you have hit submit.

And that's all there is to it. :)