Attachment files (PDF, PowerPoint, Word, etc.)
When inserting a file as attachment, you must upload one from your local machine.
Allowed file formats are: jpg jpeg gif png txt doc docx xls xlsx pdf ppt pptx pps ppsx odt ods odp mp3 mov mp4 m4a m4v mpeg avi ogg oga ogv weba webp webm
Maximum filesize is: 50 Mb
How to proceed to upload a file:
1) click on the "Add Media" icon (toolbar, second line):

2) click "Choose file" / "Upload" / "Next"
=> As result, you see the file in the text editor. When click on it, you can download it.
Pictures
When inserting pictures, you can use a file from the Internet or upload one from your local machine.
[+] Add an image from your local machine
You can upload an image from your local machine. Place your cursor where you would like to insert the image, and select the Add media icon as shown below:

A window will open to let you select a file from your local machine. Save your choice to insert your image.
Group Banner: Upload a banner image (min. size: 940 x 300 pixels | max size: 2 MB) that will be displayed on your Group's Home. Whenever adding an image, we recommend you add an alternative text and title for accessibility purposes.
Group Thumbnail: add a thumbnail image (min size: 60 x 60 pixels | max size: 512 KB) that will be displayed on all list views (related Groups), as well as the GROUPS page and on search results.
[+] Add an image found online
To add a picture from the Internet, you can copy the image and paste it directly in the editor, or copy the image location (URL). Simply right click the image with your mouse and select "Copy image URL". Depending on the browser you are using, this function can also be named "Copy Link Location" or "Copy Image Address".

Place your cursor where you would like to insert the image, and select the Image icon as shown below:

A window with image properties will open:

Image info
Paste the link you copied under URL - this will automatically generate a preview of your image. We recommend you add an alternative text to provide a description for screen readers, search engines, or when the image cannot be loaded. You can resize the image's height and width (indicated in pixels). To constrain proportions, check that the lock icon remains locked. To add a border, please add the number of pixels to define the border's thickness. By default, a border will always be solid black. You can add spacing by defining the number of pixels either horizontally (Hspace) or vertically (Vspace). Finally you can also align your image to the right or left of your text.
Link
You can add a link back to the source of the image or to another address. Click the link tab in the image properties window as shown below:

Add a URL and select the target to indicate how the link opens.
An advanced tab is also available for additional formatting.
Preview:
In the example below, we have used the following settings: width: 300, Height: 201 | Border: 1 | Hspac: 10, Vspace: 5 | Align left.

[+] The image I copied from the Internet is not the same size, why?
When you copy an online image, the original size will be copied by default. You can resize the image under the image properties.