Hi Wiilkas,
Assuming you are referring to images within your messages:
First, you need to host the image online and retrieve its URL
For example, you can host pictures here
https://imgbb.com/ for free or right-click on any image you find online
Then, while typing a new message, you need to click on the "insert image" button
This will open two tags and you place the URL between these two tags
It's a good practice to restrict the image height in the first tag like so [img height=400], or else your image may take the whole page!
Let me know how this goes, peace