While creating a Topic or Post, Select 'Insert Image'
A box pops up, click 'Select Files'
Find your image in Your Computer, and press 'Open'
After finding your image, click 'Upload File(s)'
You will now see your image in your post.
If you created a Topic, the first image in your post will become the Topic's Thumbnail
Optional, step 1:
You may upload several images at once by clicking and dragging to select them.
Optional, step 2:
You will then see all of your images, where you can rearrange them. Select 'Upload File(s).