Slim's handy guide for adding an image on your computer to a post.
Go to: https://imgbb.com/
Click the START UPLOADING button.
Select the image file you want to use. If it's very large you may wish to click the edit button and resize it.
When you see the 'Upload complete' message, click on the thumbnail. This will take you to a webpage with your image on it.
Right click the image and do "open image in new tab" (this works in Firefox and Chrome, there should be a way to do it in other browsers as well).
From the new tab, copy the URL from the address bar. Then use it to insert the image in the post editor in 'img' tags, like this:
(https://i.ibb.co/tZnn2x2/imgbbex.png)
.. hope this is useful.