Given seen people asking how to or don't know adding pics to forums as much in contest stuff and can't find a guide ill try make one.

1. Add the image to a uploader:
Imgur- easy to upload to and can stick in a album
picload - like imgur and got multiple links
trovesaurus - more trovians can view the image
Deviant art - general art spot
imgbb - basic one
gyazo - useful uploader but need to download
The forum has a image uploader but it has size limits

2. Click on the insert image above the box:
Its this symbol here -->
Itll say "please enter the URL of the image"
Most of the time the link to the image alone wouldn't work and show nothing for pc but show the image missing on mobile. So try Direct link to it
Noot: if get some type of problem try all the links available to post

3. Check and link:
Go to advanced setting if not there and preview to see if image shows. Just in case could do the image link as well just for safety

For general posting images:
If on pc you can click copy on a image and paste it in reply and it'll tend to work. other option is to use insert link.
Mobile just use the insert picture and do the link.

Art programs could use for making images:
Fire alpaca - extremely good program (free)
Gimp - number of fun little tools bit easy to use (I use this)
Photoshop - pros most likely use this and make all sorts of neat stuff
MS paint - classic

Remember you can always edit a comment to add in images and make adjustments
Also I don't want to be told "don't help the competition" I would rather see neat stuff or some color combinations. That's what helps spark reference and other ideas