Thank you for contacting us.
Yes, you can check the document at this link:
For the album, you need to select the image to upload, it doesn't get the existing image from the media folder.
I know where it is, however when I click on each topic, nothing appears. I have to right click on each topic and select open in another tab and then I can see it. but it does not show up when I just click on the topic link
We have checked and updated our documentation to fix that issue.
For the gallery image, that also depend on your number image in the album, you need to optimize the image to improve load speed.