To post screenies or any kind of picture, first you have to host them somewhere on the internet. www.photobucket.com provides free image hosting service.

Game screenies are big, both in dimension and file size, in their native form. If used without modification they will distort the layout of threads in here, so it's good to resize them before posting. I use Microsoft Paint (which comes with Windows) to do this. To take a screenie, I use ALT+Printscreen to capture the image to the clipboard. Then I paste it into a new picture in Paint. I then use the "Stretch/Skew" function in Paint to shrink the picture (setting the percentage for height and width to less than 100%, trying different numbers until the result is small but still good enough to make the point I want to make with the picture). I then save the file as a .jpg file, which is much smaller in file size than the default .bmp (.bmps are too big for internet use generally as they take way too long to load in a browser).

After I have the image resized, I upload it to my photobucket account. When you do, you will see it's link underneath it. I copy the link information, then start a post here. In the post, I put the hyperlink addy between [IMG] and [/IMG] tags and the picture appears in the post. I preview the post before committing it to the board to make sure everything is correct.