All forums have slightly different software so you'll need to persevere. First off:
- are you posting from Windows PC, Mac or phone / tablet?
- where is the picture file that you want to upload?
I've found ways to upload straight from iPhone directly into thread posts, upload to your Media folder on site & then link to it, or to post links to images already somewhere else on internet ...
If you're new at it I'd suggest going to Media and then uploading pictures from your computer to there. Separately when in a post you want to add a picture to click on the camera icon & go from there - it's two stages but perhaps easier to get the hang of.