The most popular image host is
https://imgur.com/Once you have an image uploaded, you need its direct image url. This ends in a file extension such as .jpg, .png, .gif, etc...
To post this on the forum we use the IMG tag
Once you have an image's direct url you can paste it into your post, highlight it, and click the icon circled below located above the message box:
This puts the IMG tag around your link as such, inserting the image into your post:
Code
[IMG]https://i.imgur.com/YdwPcxO.png[/IMG]