There are four ways to start this process.
The quickest is to click on "Rich Text Reply," located at the top of the Quick Post box (Thanks to Final_Fan for pointing this out). The other ways are to either start a thread, be quoting another post, or editing your own to access fonts, post images, add smileys, and do things besides post text.
If you choose to quote, simply pick a post you wish to respond to by clicking on the "Quote" button, located on the lower right hand side of the post.
Regardless of which method you chose, you'll notice that there is now a small text box to type a message in. More importantly, there is now a toolbar across the top of the screen. Go to whichever image it is you wish to use. Highlight it with your mouse, and press Ctrl+C on your keyboard to copy it. Return to the previous screen, and hit Ctrl+V to paste it.
Sometimes this doesn't work. If that's the case, find whatever image or gif it is that you want to post. Right-click on it, then scroll down to "Properties", and click on that.
This will bring up a small window called "Element Properties." Find "Image Properties" (NOT LINK PROPERTIES) and copy everything to the right of "Location:".
Take whatever you find there, and return to VGChartz. Click on the tree image in the control bar. A new window will pop up. Paste the code you copied beside "Image URL", type something into "Image Description", and you're done. Be warned that when posting gifs, the image will not animate until after you click on "Post", so don't worry if it's just a still image.
