Image block
On your site, an image content block may look like so (circled in blue):
Click on the image icon to upload an image.

How do I reorder images?
You can drag and drop the up / down arrows in the lower left corner. Or you can go to the lower left corner > settings icon > Alignment tab and click the arrows there.
How to I change the size or the images?
Go to the settings icon (lower left corner of the block) > Width tab, and adjust the width setting here.
How do I display images next to each other?
Go to the settings icon (lower left corner of the block) > Alignment tab, and set the block to Wrap, and this may display the next block side by side. Learn more about this.
How can I add a caption?
Move your mouse over the image, and then click on the edit icon. Add the caption in the Settings tab.