It's pretty simple to post art here. The first thing you need to do is host your art somewhere. Do you have a Deviantart or Imgur account? These are just two of many examples of where you can upload your art.
Once you have a place that you post your art online, simply create a topic in the appropriate section (LBT art goes in Fanart And Fanfiction and non-LBT art goes into The Arts-Visual Art). Post a link to your art and post the topic and there you go.
If you want to make the pictures visible on this board like some people do, then what you need to do is same thing that I described, but you need to, instead of providing the regular URL link, you need to right-click on your picture and click Copy Image Location or whatever it tells you. Paste that in the URL just to make sure it sends you to only the picture. Once you have that, paste that into the message of your topic and enclose it with [ img] at the left end and [ /img] on the right. This should make it so that, once you post the topic, the image shows up. Make sure to remove the spaces between the [ and i, and the [ and /; I had to add them in order to post this.
Word of warning, however. Make sure that the images are not huge in size. While you can resize them on Deviantart and other places for example, you can't resize them within this messageboard, so if you post a huge image, it's going to be really hard for someone to look at it easily. So make sure that they are small. 1,000 x 1,000 pixels should be fine, perhaps larger and smaller, too.
I hope this helps.
