Open your calendar section from the menu bar on the left.

In the upper right corner, click on the + New Post button.

The creating post box will be displayed.

Then, at the bottom of the creating post box, you will see a few different icons. Click on the second one – the image one.

You can choose whether you want to drop the files, paste them, browse the device, or give a link to the file

Finally, confirm your choice and wait until the file will be uploaded.