Go to the Commons tool.

Select the Commons tool from the Tool Menu of your site.
Add text.

Enter text into the editor.
Add a link. (Optional)

- Select the link button (Insert a link).
- Enter a caption for the link in the Display text field.
- Enter the URL in the Link to field.
- Optionally activate Load thumbnail to generate a small thumbnail preview of the linked page.
- Select Insert.
Add an image. (Optional)

- Select the image button (Insert an image).
- Select Choose File to locate and attach an image file from your device.
- Select Insert.
Click Post.
